Per
https://www.hilton.com/en/hilton-honors/support-faq/
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 at midnight. 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.
Emphasis is mine. If you cannot carry it forward, what is "leftover". My understanding has always been what you dont use at dinner that last day, goes to breakfast the next morning