The advice IAHtraveler gave you is sound. Schedule changes can happen at any time and you should not expect CO to notify you. So definitely check periodically. However, there are some reasonable expectations.

1. Expect bookings far in the future to experience schedule changes more so than those less far out. (Still possible! But less likely.)
2. At the risk of stating the obvious, expect bookings with connections to experience schedule changes (there are more flights involved).

My opinion: Unless something unusual happens, I'd be surprised if the schedule of a Memorial Day weekend flight is changed after March 31. Still possible! But not likely.