Regional Stuff: 1 hr before ETD:
Preflight Checklists, etc -- 40 mins until ETD/Pushback External Walkaround -- 30 mins until ETD/Pushback (FO) Sign off on DIspatch Paperwork -- 25 mins until ETD/Pushback Start Boarding -- 20 mins until ETD/Pushback End Boarding -- 4-5 mins until ETD/Pushback (If there are late pax, then...)
Start Pushback -- 1 min until ETD/Pushback (I personally like to be a little early, especially at congested airports where I know we can get delayed on the ground)
P.S. I don't know what other airlines do, just our general procedures.
Hope this helps,
Andrew