You set a set of credits per person, per night of your stay, not per day. So 7 nights = 7 sets of credits, 14 nights = 14 sets of credits etc.
They can be used as you like, in any order and quanitity that you like between the time you check in and midnight on the day you check out.
For most people check in day is travel day, so they won't use their whole allocation for that night, leaving some left for check out day. On the qsdp, we'll probably use 3Qs and 2 snack credits on check in day as we're not all that hungry, leaving 5 QS and 6 snack credits to carry over/use on check out day.