Send windows and timezones
TL;DR
- The evidence here is the weakest in the whole library. "Tuesday to Thursday, 9-11am" is repeated everywhere and rests on almost nothing you can check.
- The part that survives scrutiny: send inside the recipient's working hours, in the recipient's timezone. Everything finer than that is unproven.
- Pick a window, hold it constant, and spend your testing budget on the list and the offer instead.
Why this page is short on numbers
Most timing advice traces back to a handful of vendor blog posts that quote each other. When you follow the chain to the most-cited source, it declines to give a universal answer: its conclusion is that "it's our target group that specifies the best day and time for email delivery", and the one survey figure it does carry points the other way — 91% of recipients said they did not mind receiving email in the middle of the night (vendor blog, updated 2025) [1].
That is worth stating plainly, because the confident version of this advice is everywhere and there is no independent corpus behind it. No counter-school exists either — not because timing has been settled, but because nobody has published a study serious enough to argue with. Treat every "best time to send" number, including any you find in a tool's UI, as folklore until someone shows you the sample.
What does hold up
Timezones, not clock times. A 9am send from your desk is a 3am send for a prospect five timezones east. This is the one part of timing with an obvious mechanism: an email that arrives overnight sits under everything that arrived after it. If your list spans regions, schedule by the recipient's local time — sending platforms support this, and it is the single timing setting worth configuring carefully.
Working hours, loosely. Business email gets read during business days. That narrows the useful window to roughly Monday to Friday in the recipient's region, which is about as far as the evidence carries.
Consistency beats optimization. Reputation rewards a steady sending pattern, and holding the window constant is also what makes every other test readable. If your send window drifts while you are testing subject lines, you cannot attribute the difference — see A/B testing.
Practical default
Weekdays, mid-morning in the prospect's timezone, spread across the window rather than fired at the top of the hour — see Throttling and rotation. Then leave it alone. If you want to test timing anyway, test it as a proper split with everything else held constant, and expect the effect to be small enough that you will need a large list to see it at all.
References
- Woodpecker — The optimal time for cold email delivery (vendor blog, updated Jan 2025)