Many of the airlines have alerts you can set up...go onto the website for your airline and see if yours does. I have AA set up to alert me via e-mail and text message if our flights change. And that's ok for last minute, but I also check the day before and the day of to confirm our flight times online.
BTW, if they change your flight time you can always call them and tell them the new time is no good (if it's not in your favor) and tell them what flight you'd prefer to be on. They will generally change you with no fee!