As a GM I was aware that this was a benefit. I have a flight this week LAS-ATL at 3pm. Because of a change in plans I wanted to change to the 11:30 redeye. There are many more seats available on the later flight so I didnt think it would be a problem. I called the rep who said I could only reserve the seat within 3 hrs of the flight. This means I would have to miss my earlier flight and wait until 8:30 to see if I could get a seat. I could however change now for the $150 fee. This makes no sense to me. It would just be a wash, the redeye actually is in less demand. I travel somewhat frequently and have been loyal to Delta but have not ever tried to make a change such as this. Could someone who is more familiar with these things tell me if I am missing something.