Off peak hours can be set for each calendar, and a different hourly rate can be set for those hours on that calendar.
Each calendar can have a timeframe for off-peak hours (e.g. 11pm-5am), in order for the off-peak rate to apply automatically when a client creates a booking in that window of time.
Set, remove, or edit off-peak hours and the rate
Go to Kitchen Settings > Calendars > pencil icon to edit
In order to have the hourly rate "trump" the off-peak hour rate instead, simply remove any off-peak hours from each calendar's settings by unchecking the box. With no off-peak rates, the hourly price of the calendar will take precedence.