USFS policy it to cancel the reservation if they don't show up within 24 hours: "No Shows:
Reserved campsites and group overnight facilities will be held until check-out time on the day following your scheduled arrival. " - https://www.recreation.gov/marketing.do?goto=/acm/resPolicies.htm
Sometimes people want the flexibility to extend a day at one location, and get in late to the next - not everyone wants to be locked into an exact schedule. Sometimes things happen (e.g. breakdowns) on the road, and you don't get to where you expected to on time. Or maybe they just wanted to come in before checkout time the next day and be assured a spot. Just because they weren't there when you left in the morning doesn't mean they were no-shows. I think the policy above is a perfectly reasonable compromise.
