I am confused about Hilton's cancellation policy. See below from a recent Hampton Inn reservation:

"This reservation can be held until 6PM on the check-in day, or guaranteed with a credit card for late arrival.
If you wish to cancel, please do so 24 hours prior to arrival to avoid cancellation penalties."

How is it that that they only hold the room until 6pm the day of arrival if there is a 24 hour cancellation policy? Does this type of policy mean that in order to get more flexibility I should avoid holding the room with a credit card and just call the property myself before 6pm the day of arrival if I will arriving late? Or would the entire reservation then disappear 24 hours before leaving me without a hotel room? How would they enforce the 24 hour penalty rule if I didn't hold the room with a credit card, or would that rate simply not have been available when the reservation was placed?

What is the actual definition of 24 hours before - is it 24 hours before the hotels stated check in time (usually 4pm)? I tried to cancel a Double Tree reservation made on the web a few weeks ago that had a 24 hour cancellation policy. The reservation was for a Sat night arrival, and I tried to cancel it on Friday afternoon, but I was unable to cancel it on the Hilton website. The web support number told me that I had to ask the hotel directly (incidentally, the hotel did allow me to cancel penalty free).

Before you all blast me, I do not frequently cancel rooms, but their are inevitable changes of plans and I would like to understand the rules better.

Thank you,
BJFly