Using New Outlook on Windows for personal email, calendar, and contact management
I found it on New Outlook on my Mac.
Outlook -> Settings -> Composing -> "Undo Send: Wait to send messages for ___ seconds".
I was able to change mine from 20 seconds to 0 seconds, which eliminated any delay for all emails. You could reverse this and change from 0 seconds to 10 or 20 or whatever. Hope this helps!