Just a warning however, even though the credits don't expire until midnight of the day you check out we have had problems in the past with the credits not appearing available on our card after check out.
Fortunately we had an experienced server who had seen this before so she knew to ask us if we had check out that morning. The restaurant (Kona) took great care of us and got the credits re-stated onto our card but it did take about 15 minutes for them to get it cleared up. Fortunately we were dining at a very slow time so the waitress and the manager had time to deal with it.