Feels kind of sleazy to go into the playoffs with a 28-man roster. They could at least set it up so that you have to (and can) drop players to get to 25.
You can but every move has to be done before then. It is in the rules and also you live and learn. I have asked the cut off question many times as I have forgotten almost as many minus 1. I just dropped my worst starter and a bad offensive player just before the 142 game started. In another League I didn't get to it in time and I am stuck with bad players.
Set your bad batters not to face LHP or RHP and do the same with your Pitchers along with not used before the 9th inning. They will see little time during the game.