You get 8 nights, but you can use them over the 9 days. Your credits start when you check in and last until midnight of the day you check out.
Here is what we did 6 nights, 5 days of tickets:
Day one - check in, no parks, one CS for supper
Day two - park, 1TS, 1 CS
Day three - park, 2 TS
Day four - park, 1 TS, 1 CS
Day five - park, 1 TS, 1 CS
Day six - park, 1 TS, 1 CS
Day severn - checkout, no park, 1 CS (though we had some left over b/c we had split some, so you could technically use them and all your leftover snacks up on your last park day.)
Hope that helps!
