I think it might be more interesting if there was no option to relisten to the message before sending, edit, delete it, etc. Or at least this could be one possible option for the braver ones/those preferring spontaneous messages.
It would be a one-time deal and once you've started recording, it would be sent once you've finished recording. And then it would be no way you could hear it earlier than the date you've indicated, the service should make sure of this. If you've f*ked up during the recording process, this would also be a funny thing to listen to your future self.
The date of delivery should then better be indicated before the recording, for the users to not try to cheat after and indicate a proximate date if something they perceive as failed recording attempt happened.
This could possibly be applied to writing as well, e.g. you couldn't go back and fix the text, but it's way easier and better with sound or video recordings, it would be like those voice message recording functions of texting apps where you hold the button for as long as you talk and once you release it the recording is sent and you can't undo it, it brings more spontaneity and liveliness to the process.