How do I test the best time to send emails?

You've probably read some blog post that says "Tuesday at 10am is the best time to send email." And maybe it is. For someone else's audience. The only way to know what works for yours is to test it yourself.

But Here's how to set up a send time test that actually gives you trustworthy results.

Pick two or three time windows to compare

So Start with clear contrasts. Morning vs afternoon is a good first test (say, 8am vs 1pm). Weekday vs weekend is another useful one if your audience is mixed. Don't test five windows at once. Two or three is enough to learn something real without splitting your list too thin.

Divide your list randomly

Send the same email content to each group, just at different times. The key word is randomly. If you assign groups by last name, signup date, or any other pattern, you'll introduce bias and the results won't mean much. Most ESPs like Mailchimp, Klaviyo, or Brevo have built-in A/B send time features that handle the random split for you.

Should you run tests in parallel or sequentially?

Parallel is better. Sending both groups on the same day (just at different hours) removes the noise of "was it a weird Monday" or "did something news-worthy happen that week." Sequential testing, where you test one time this week and another time next week, makes it harder to separate timing from external factors.

How long should you run the test?

At least four to six sends at each time window before you draw conclusions. One send isn't enough. Email open patterns vary week to week based on holidays, news cycles, your own content, and a dozen other things. Running the same test across multiple campaigns gives you a real signal instead of a lucky result.

What to measure

Open rate is the most directly affected by send time, since it reflects when your email was sitting at the top of someone's inbox. Click rate and conversion rate matter too, but don't ignore the open. A high click rate on a low open rate can be misleading.

One thing the "best time to send" articles almost never mention: time zones. If your list spans multiple regions, 8am for your Boston subscribers is 5am for someone in Los Angeles and 1pm for someone in London. Consider segmenting your test by time zone, or at minimum, note what percentage of your list is outside your sending timezone. Tools like Klaviyo and Brevo have smart send-time features that can handle per-subscriber local time delivery if you want to skip the manual work.

Segment your results before declaring a winner

But your B2B subscribers (checking email between meetings) may behave completely differently from your consumer subscribers (scrolling at lunch or in the evening). A single "winning" time might be masking that one segment loves 8am and another prefers 7pm. Pull the data by audience type if you can.

And once you find a winner, keep testing every few months. Your audience's habits change, and what worked in January may not hold in August.

Want to go deeper? Read about send time optimization (STO) for how platforms automate this, or check out testing sending frequency once you've nailed your timing.