Does anyone have insight as to what exact time is meant by the 24-hour cancellation policy seen for some properties? Below is the exact phrasing of the cancellation policy:

"If you wish to cancel, please do so 24 hours prior to arrival to avoid cancellation penalties."

What is "arrival"? Is this a standard time, like earliest possible check-in time, so I would need to cancel T-24 from, say, 3 PM? It's often the case for me and I assume as well for other Diamonds to arrive late at night or even past midnight to check in, so to me 24 hours prior to check-in might mean 11:59 PM on the day before arrival.

In practice, on the day before arrival I find I'm unable to cancel online starting sometime in the late afternoon but am able to cancel even late in the evening by calling the property directly.