The time you ask someone to hold open should be treated as something they are giving you.

Held time has a cost even when nothing happens inside it. The evening kept free, the morning blocked, the trip not booked are all real things declined on your behalf, and because they are invisible they tend to get spent carelessly. Cancelling late is not a neutral act. It uses something that was already given.

Ask for held time deliberately and release it the moment you know. Say thank you for the hold itself, not only for the meeting. When you must cancel, do it early and name what it cost them.