For our use case of MS bookings we really need to use multi-day bookings as the service the user is selecting can be undertaken at any point in the selected week.
So a user will open the bookings calendar, select the service (in our case a certification attempt), they will then see that only Mondays are selectable as start days (no time selectable as it is a multi-day service)
We have a single virtual staff member assigned to this service. The service however should not be available every week and the easiest way of limiting the service availability is to create a calendar entry within the virtual staff members' calendar, this way we can use the power of recurring appointments to easily influence the availability of the service.
Unfortunately due to the fact that personal calendar entries do not affect all-day/multi-day bookings, this does not work.
Keep in mind that when using the all-day and multi-day feature, the Office 365 calendar availability for your staff members does not work like it does for shorter services. We assume that you want your customers to be able to book you for valuable, longer-term services even if key staff have short, personal conflicts on a day that a customer needs you. This means that staff members can be booked for that service even if they are busy with short, personal appointments.
My improvement request is to allow staff calendar availability to affect all-day/multi-day services in the same way it influences shorter services.