Randomizing email send times can be very powerful for a number of reasons.
First, it applies to Einstein's Theory of Insanity; "Doing the same thing over and over again and expecting a different result". If you always email Sarah at 9:00AM on Tuesday and she happens to be a late night person, you'll likely get buried under the countless other emails she received that day / week. By randomizing your send times, you're sampling her to see when she'll engage. So, it's creating unbiased data on the individual recipient's habits.
Second, it can help with email deliverability because you're not flooding receiving servers.
Third, we've done extensive testing on this and as part of those tests, even randomizing everyone on a list over 24 hours will slightly outperform sending to everyone at once (blasting).
With Seventh Sense, anyone who has historically never engaged with you, the system will pick a randomized send time for these individuals within the provided delivery window.
If you're not scheduling the delivery over at least 24 hours and someone has never engaged within the delivery window, the system will pick a randomized time for those individuals.