Rated 5 out of 5 stars

Many, many times I have been glad to review an email, even 15 minutes before it goes out.
And I use it to schedule emails long times ahead, getting the job done early.
I do suggest an option to send a notice back to me before an item is sent, when it is scheduled for a longer time ahead.

This review is for a previous version of the add-on (6.3). 

I filed an enhancement request, though I don't know when I'll get to it:

https://github.com/jikamens/send-later/issues/10

You can subscribe to that issue if you have a Github account and get notified if/when I am able to do something with it.