Elaborating on what Cafeen posted, you get credits according to how many NIGHTS you stay, not how many days (you will receive 2 CS and 2 snacks per person per night you stay), and you get them in one lump sum when you check in - then it's up to you how you use them. If you want 2 credits to use on your last day, you need to plan to make sure you have that many credits left over to use on that day.
So if you have 2 people staying 3 nights, at the time you check in your dining account will have 12 CS and 12 snacks to be used before midnight after you have checked out.