Why cap billed hours?
When a vehicle has an hourly rate, every hour of use is billed by default. Keeping the vehicle for a whole day would then count as 24 hours, even though it mostly sat parked overnight.
The daily cap lets you recognise that nobody really drives around the clock. You set a maximum number of hours billed per day, and each day where use exceeds that number is brought back down to the cap.
Good to know: This setting only matters if the vehicle has an hourly rate. If you bill by the kilometre only, it changes nothing.