No, you will not be reimbursed at check-in. If have a package with Disney and you are more than 45 days out from check-in you need to call 407-WDISNEY (or contact your travel agent) and ask them to modify your package for the correct number of ticket days. So, if you currently have a 5 day park hopper you need to ask them to change it to a 4 day park hopper. If you are within 45 days from check-in you can still call & try to change it, but you are within the penalty period and the change fees may be more than you are saving by reducing the days on your tickets. If you bought tickets by themselves I’m afraid you will just have to go with the number of days you purchased as tickets are non-refundable.