I would go with 11:55 a.m.
If you do a search, you'll find people bragging about how quickly they got off ship, how soon they got onto transportation to the airport, how early they arived at the airport, and how rapidly they passed through security.
But do you really want to count on everything going perfectly?
For a 10:25 a.m. flight, you would need to get to the front of the check-in line at the airport before 9:25 a.m. to check your bags. (I don't think they'll check your bags at the port for a flight that early, even if your airline is represented at the port.)