And here Gugol pleased us:
Gmail Custom Time ™
It turns out that from yesterday Jimail can send letters at a specific time. Even in the past.

This was done so that employers or parents (emphasis is placed on the latter) could be told (preferably with a slight indignation in their voice): “Mom, I sent you this letter 5 hours ago! And haven’t you read it yet? ”The
very principle of working and calculating the reason why no more than 10 letters can be sent is very interesting. You can learn more about this on the official Gmail Support page. Come on ...
If someone with English is not as tight as mine, then please write a more detailed report on the work of the service. I will publish it here, with attribution, of course!
It turns out that from yesterday Jimail can send letters at a specific time. Even in the past.

This was done so that employers or parents (emphasis is placed on the latter) could be told (preferably with a slight indignation in their voice): “Mom, I sent you this letter 5 hours ago! And haven’t you read it yet? ”The
very principle of working and calculating the reason why no more than 10 letters can be sent is very interesting. You can learn more about this on the official Gmail Support page. Come on ...
If someone with English is not as tight as mine, then please write a more detailed report on the work of the service. I will publish it here, with attribution, of course!