When you add a day to a park hopper, do you have to do it the day before your last day or can you do it on your last day? For example, if one has a 4 day hopper and may want to upgrade it to a 5 day, would it have to be done on day 3 before day 4 is even used, or just before the end of the day on day 4? If we decide to add a day, just want to make sure we have the timing right.