Hi there!
I have several youcanbook.me accounts and on one particular account it just won’t let me to change my durations of the bookings. The link simply isn’t there.
How can I solve it? 
The duration of the booking is set under Times & availability > Duration & display. What do you see when you navigate there?
it wasn’t there before, so I had to log out and log in again. That worked.
However my calendar display shows some unavailable time slots even though the calendar it is synced to has no appointments in it. Could you help with that?
it looks like there are busy events on that Google calendar at 1 and 3pm. If there is nothing on your calendar, check that there aren’t any declined invitations (more about that here) You can find other troubleshooting tips in our knowledge base!