Availability in MS Bookings not correct

In our bookings portal, we set-up a service with 2 staff assigned.

The first staff memeber is available, the second one is on holiday (time off)

We have made this set-up in the back-end.

If there is a booking on that day already sheduledfor staff number one for let's say 10h, It will still show this time on the front.

It looks like it doesn't count the time off from the second staff