We booked the 7:20 flight for December almost as soon as it was announced. Wouldnt you know it, a couple weeks later it was gone and we were on the later flight. At first I panicked and called just to get confirmed seats so we would all be together(flying with 2 young kids). So technically, we accepted the later flight. After calming down for a few days I thought a little straighter and we decided to leave a day earlier as to not cut our first day short. We called again and had no problem changing to a day earlier. They worked with us and there was no extra charge for the change even though the prices of the flights had gone way up by then.
I would say decide what your preference is then call and see what they can do for you. Hopefully you will be as lucky as us.
Also, we were origianlly booked on AA. They cancelled our flights, gave us new ones, now connecting, later times, and on tiny planes(which I refuse to fly). We were able to get a full refund there.