I use the 5th night benefit all the time. Sometimes I actually want 5 nights, but often times only need 4 but still get the 5th, like you wanted. I usually travel with kids and the ability to shower and brush their teeth and then leave at 8pm has value to us (just dont tell the front desk you are leaving early).

15k points is a small price to pay for a guaranteed super late check out, if that is something of interest to you.