If you can’t figure out a native KM way to do this, the following AppleScript works for me (I’m on KM11 and Ventura).
tell application "Mail" to activate
tell application "System Events"
tell application process "Mail"
click menu button 1 of group 1 of group 1 of toolbar 1 of window 1
repeat until exists menu item "Send Later…" of menu 1 of group 1 of toolbar 1 of window 1
delay 0.1
end repeat
click menu item "Send Later…" of menu 1 of group 1 of toolbar 1 of window 1
end tell
end tell
I found this by making a new blank email, keeping this as the front window in Mail and using the new KM11 "Scan Front Window of:" in the Press a Button Action:
I've only learnt how to do this today. It scans only the front window of the Application so, you need to have the front Window as a Mail Message for that button to be found by KM.
Glad to help, and kudos for writing up the walkthrough.
Somebody marked my post as the solution, but feel free to unmark it and mark a different post as the solution if you’d like since you went the native KM route.
on third thought, I prefer your solution which goes directly to the send later ... button menu item. Other solutions simply display the button menu.
Yes I could follow the button menu action with down arrows and enter on the correct menu item, but it's not as elegant as your solution