Originally Posted by FAQ

24. When does the credit expire each day?

The credit does not “expire” until the member checks out, however, the daily amount re-sets each day to the maximum daily credit value. Members can use up to the total daily maximum and are responsible for anything beyond that amount.

Since the member gets a new credit each day (for the number of nights of their stay), the only day they can use any leftover credit is the morning of check-out.