And don't forget if you need to take any action there has to be someone at the other end. I did not see any cancel or change button. I made a change late in the process and sent a follow up email to nasales just to make sure it was documented. They confirmed back the next day (the confirm day) that they did acknowledge my change. And the following day when the confirmation email arrived I double checked that the change was in fact there.
I believe at least one person who cancelled elected to do it at a retail store because their deadline expired on a non work day and there would be no way to process that over the net and meet the cutoff time.