Preference Timezones & Send-Time Optimization: Mastering When to Talk to Your Audience

In the fast-moving world of digital marketing, timing matters more than ever. You may have brilliant copy, beautiful design, and compelling offers—but if your message lands when your audience is asleep or distracted, most of your work is wasted. That is where preference timezones and send-time optimization (STO) become powerful levers: they move your message into your recipient’s “golden moment” when they are most likely to open, read, and act.

In this article, I’ll walk you through why these techniques matter, how they work, and how to apply them in your campaigns—rooted in recent data, real tools, and strategic thinking. As Mr. Phalla Plang, Digital Marketing Specialist, I believe your message deserves a moment when it can shine.

Why Preference Timezones Matter

When marketers talk about “best send time,” too often they speak in broad strokes: “send emails at 10 a.m.” or “worst time is after 6 p.m.” These general rules may help a bit, but they ignore two key realities:

1. Audiences are global. If your list spans multiple countries or regions, sending at 10 a.m. in New York might mean 2 a.m. in London or midnight in Tokyo.
2. Individual users have unique habits. Some people check email early in the morning; others at night. Some open only during work hours; others in evenings.

Preference timezones address the first challenge: ensuring your email lands in the local time window that makes sense for that audience. Send-time optimization addresses the second challenge: customizing when within that window each recipient is most likely to engage.

The challenge of global sending

If your audience is spread across time zones, a single send moment will always disadvantage some region(s). For example, when it’s 9 a.m. in New York, it’s 6 a.m. in Los Angeles, 2 p.m. in London, and late evening in Asia. Those on the tails might ignore your message (or not see it). (Litmus, 2016) Litmus

To counter this, marketers use time zone sending—segmenting sends by user’s time zone (or inferred locale) so each subscriber receives the email in their morning or day. Tools like Marketo’s “recipient timezone send” feature attempt this. theseventhsense.com HubSpot also supports “optimize send time per contact” with timezone awareness built in. HubSpot Knowledge Base

But simply matching local morning hours isn’t enough. That is where Send-Time Optimization (STO) steps in.

What Is Send-Time Optimization (STO)?

Send-Time Optimization (STO) is the technique of using historical engagement data to deliver each email to each recipient at the moment they are most likely to open it. Rather than one blanket schedule, STO personalizes the send moment.

Many platforms now support STO. For example:

• Mailchimp offers a “Send Time Optimization” mode: it picks the optimal hour in the next 24 hours for each recipient based on past engagement. Mailchimp
• HubSpot allows “optimize send time for individual contacts,” calculating times from past opens and clicks over up to 90 days. HubSpot Knowledge Base
• Higher Logic describes STO as analyzing each contact’s history to figure out the best deliver time. Higher Logic
• Netcore Cloud’s AI-driven STO engine sends email copies to different users at different times, based on opening patterns. Netcore Cloud

How STO works (in simplified form):

1. Gather historical data: your email system tracks when each contact opened or clicked past emails.
2. Analyze patterns: it finds the hour-of-day or time window when a contact is most active.
3. Predict optimal send time: for a new campaign, it assigns a tailored send moment to each user within a allowed window.
4. Continuous learning: as more data comes in, the model refines its predictions.

This approach helps the email arrive when the inbox is less crowded and when your recipient is primed to respond.

Some advanced approaches in academic research even model “time to open” using machine learning (e.g., recurrent neural networks in a survival model) to better predict when a recipient will open given different send times. arXiv

Why STO + Time Zones Outperforms Blanket Timing

Let’s compare three approaches:

• Uniform sending: send everyone at 10 a.m. your time.
• Time zone sending: deliver at 10 a.m. local time for each user.
• Time zone + STO: send around local 10 a.m. but customized per recipient within that window.

Uniform sending fails for global lists: many users will get your email at odd hours, lowering open rates.

Time zone sending helps a lot more: everyone gets your message in a reasonable local window. But it still assumes each person is equally likely to open at, say, 10 a.m.—which is often false.

Time zone + STO is the sweet spot: segmenting by locale and personalizing the moment. This maximizes the chance that each message arrives at the right time for each user.

Real-world brands using STO often report 5–10 percent increases in open rates just from timing improvements (Emarsys case of Puma Europe) SAP Emarsys

What Does the Data Say? (Updated Benchmarks)

Let’s look at recent email timing benchmarks to understand patterns—but remember: benchmarks are starting points, not universal truths.

Open rate peaks by time of day

• Omnisend (2025): peak open rates at 8 p.m. local time (59 %) followed by 2 p.m. (45 %) and 11 p.m. (40 %). Omnisend
• Bloomreach: In Asia-Pacific, business-hour sends (9 a.m.–6 p.m.) do well, but some click peaks at 11 p.m.Bloomreach
• Twilio / SendGrid: among Holiday sends, 7 a.m. saw strong engagement; but they found no single statistically dominant hour overall. Twilio
• OptinMonster (2025 overview): most email performance peaks between 9 a.m. and 11 a.m., with secondary peaks in early afternoon and early evening. OptinMonster

Best days of week

• Many studies point to Tuesday through Thursday as top days for open rates and engagement. (Omnisend, OptinMonster, MailMunch) Omnisend+2OptinMonster+2
• Friday often shows strong clicks or conversions but weaker opens in some data sets. (Omnisend) Omnisend
• Weekends are more variable. Bloomreach notes weekend open peaks (Saturday 7 a.m. / 9 a.m., Sunday at 9 a.m.), but fewer campaigns land on weekends so sample sizes are smaller. Bloomreach

Key takeaway

These benchmarks suggest that mid-morning (9–11 a.m.) and early evening are often good windows. But extremes also work—some audiences open late nights or early mornings when inbox competition is low.

However, because individual behaviors diverge, using benchmarks as presets risks missing huge engagement gains. That’s exactly why STO + time zones is so powerful.

How to Implement Preference Timezones & STO in Practice

Here’s a step-by-step guide to putting this into your email marketing workflows.

1. Collect and validate location/time zone data

• Ask users to provide location or time zone (during signup or in profile).
• Use IP-geolocation or inferred locale from addresses.
• Clean and validate—avoid wrong time zone assumptions from VPNs or proxy servers. (Marketo warns about VPN distortion) theseventhsense.com
• Segment your list by broad time zones (e.g., UTC offsets or region bins) as a starting point.

2. Audit your historical send and open data

• Pull reports of sends, opens, clicks by hour for each contact (or groups).
• Look for patterns: maybe many openers cluster at 8 a.m. or 7 p.m.
• Ensure enough sample size—STO systems often require minimum data volume before recommending times.

3. Enable or adopt an email tool with STO

• Use platforms that support send time optimization: HubSpot, Mailchimp, Netcore, Emarsys, others.
• In those tools, turn on the feature (e.g., “Optimize send time” per contact). Mailchimp+2HubSpot Knowledge Base+2
• Choose the allowed time window (e.g., 8 a.m. to 8 p.m., or up to 24 hours).
• In large sends, use throttling (spreading sends across hours) to reduce server load or avoid spikes. (Higher Logic supports throttling) Higher Logic

4. A/B test to validate results

• Run controlled splits: one group with standard send time, one with STO/time zone mode.
• Measure opens, clicks, conversion lift.
• Over 2–4 weeks, ensure statistical significance.
• Adjust windows or rules if STO times seem off.

5. Continuously refine and monitor

• Update your models as user behavior changes (holidays, daylight saving, seasonal shifts).
• Check for contact segments whose behavior is anomalous (e.g., night-owl crowd).
• Use fallback rules for contacts with insufficient history (e.g., send at a default time).
• Monitor deliverability: sending at odd hours shouldn’t hurt deliverability—but watch for ISP rate limits.

6. Combine with content and segmentation

• Timing is one factor—relevance of content, subject lines, sender reputation, and segmentation still matter greatly.
• For example, for a B2B audience, mid-morning weekdays might dominate. For B2C (night shoppers), evening or weekend sends might outperform typical business hours.

Real-World Example: From Theory to Practice

Suppose your company runs email campaigns to subscribers in the U.S., U.K., and Southeast Asia.

• You segment lists into Eastern Time (U.S.), GMT (U.K.), and Indochina Time (Cambodia/Vietnam).
• For each segment, you set a broad local window: say 8 a.m. to 8 p.m. local time.
• Activate STO so each subscriber’s send moment is optimized within their window.
• You run an A/B test: half of U.S. list gets classic 10 a.m. EST send; the other half gets STO-enabled.
• Over several campaigns, you see STO group open rates 6% to 9% higher than static sends.
• You further refine by noticing that Southeast Asia users often open emails around 9 p.m., so you widen their window in future campaigns.

Because you respect both time zones and individual behavior, each message lands at a more opportune moment.

Pitfalls, Limitations & Best Practices

• Insufficient data: STO models require history. For new subscribers, fallback to defaults.
• Irregular habits: some users open at random, so predictions may be weak.
• ISP throttling or constraints: sending many emails at odd hours can run into deliverability issues or mail server limits.
• Localization differences: cultural or working-hour norms differ (weekends, holidays).
• Mis-inferred time zones: VPNs, mobile devices, or data mismatch can mislead your assignment.
• Overfitting: if your model is too sensitive, it may chase noise rather than stable patterns.

Best practice tip: start with a narrow window, measure carefully, and expand over time. Always combine timing improvements with content quality, segmentation, and deliverability hygiene.

Why This Matters for Your Marketing ROI

• Higher open rates: landing in the inbox when the user is active means better visibility.
• Higher click-through and conversions: timing + relevant content = more action.
• Better send reputation: fewer “ignored” emails means fewer negative signals.
• More efficient list engagement: you reduce wasted sends to low-probability users at bad times.
• Scalability: as your list grows global, you don’t need manual scheduling per region or group.

As I always say, “Your message deserves a moment when it can shine.” — Mr. Phalla Plang, Digital Marketing Specialist

Conclusion: Timing Is Personal, Not Universal

In a world flooded with messages, the power lies not just in what you send—but when you send. Preference timezoneslet you respect where each user lives, while send-time optimization lets you respect how each user behaves. Together, they transform your email strategy from guesswork to precision.

Yes, benchmarks like 9–11 a.m. or Tuesday-Thursday are useful starting points. But your real gains will come when you tailor sending moments per person, based on their unique habits. Use the tools at your disposal, test carefully, and evolve your model.

Your content matters. Your deliverability matters. But in many cases, the difference between “sent and forgotten” and “opened and converted” comes down to one factor: the right timing.

References

Emarsys. (2025). Is there a best time to send marketing emails? Emarsys Blog.
Higher Logic. (2025, September 8). Send Time Optimization. Support article.
Litmus. (2016, July 14). International Email Marketing: How to Master Time Zones.
Mailchimp. (n.d.). Use Send Time Optimization.
Netcore Cloud. (2023, March 6). Send Time Optimization: A simple guide for email marketers.
Omnisend. (n.d.). The Best Time to Send an Email (2025 Research).
Twilio. (2025, June 24). The Absolute Best Time to Send Email Campaigns in 2025.
OptinMonster. (2025, July 24). The Best Time to Send Emails in 2025 Revealed!.
Seventh Sense / The Seventh Sense Blog. Marketo Timezone Sending vs. Send Time Optimization.
Singh, H., Sinha, M., Garg, S., Banerjee, N. (2020). An RNN-Survival Model to Decide Email Send Times. arXiv.