The Booking Charge Slot setting lets you define the minimum chargeable duration for a booking. If you would like to charge for a full hour's duration for any booking that takes less than an hour, you can do that using this setting.

You can find the setting in the Settings > Platform Modules > Calendar & Bookings tab. There are three options that you can choose from - 15 minutes, 30 minutes, and 1 hour.
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Depending on the minimum chargeable slot chosen, a booking will always be charged for at least the minimum duration chosen. E.g. If you select the minimum booking charge slot to be 1 hour, members may book for less time, but they'll still be charged the 1-hour price: This setting is respected for both booking fees and booking credits/coins usage.