I received advice that the apportionment of expenses for occupancy rate is not related to the days booked, but rather the days the room was available for bookings.
Some times of year bookings are slower, others they come thick and fast. There are days in between bookings for room cleaning/guest turnaround and so on. All of these days incur expenses despite not generating income on that day.
I guess you will run into problems if you are only a casual host and only occasionally accept bookings when it suits your private life. In that case it may be appropriate to only claim expenses based on days occupied.
The situation is slightly different for a Mixed Use Asset with more than 62 days empty a year (by empty I mean totally empty such as in the case of a holiday home that is rented out for part of the year, privately used for part of the year and empty part of the year).
Floor area mixed use apportionment applies to the home you live in and share with guests.