We have our configuration with Enable Time Slots and Time Categories also, because some Categories we would like to be in hours and others in days.
We created a Listing in the categories that is time slot, but when adding Price Extra I only have to options:
If you switched to time slot bookings, then the price per day basically means price per time slot (e.g. hourly price if the time slot duration is 60 mins). There are 3 possible pricing modes for extras:
per hour
per booking (doesn’t change no matter how many slots are selected)
per place (if multiple places per booking are enabled in settings)
These are the only options available for price extras at the moment.