While I am composing a message,
many
times I would want to be reminded if I don't get a reply within a certain time.
So there should be a shortcut that lets me "Send and Snooze" (with "Only if Nobody Replies" ON as default) in one shot, OR the Snooze option within the Composer window - especially since you already have a "Send Later" next to Send which is similar but different! :-)