My long range reservations change continually, mostly by a few minutes or so. As an Elite member, I do get notices if it is a significant change. The airlines I fly (DL and AA) will send an email or phone message if you tell them to by using the notification part of their website.
Be aware however, you can get inundated with messages. I was once returning from the Left Coast and was already aboard a delayed flight. Every 15 minutes for about an hour, I got a phone call that the flight was delayed.
Cheers