Appointments+ available slots change based on service type

I have 3 services, with 3 durations:

1hr Service A = 60mins
2hr Service B = 120 mins
3hr Service C = 180 mins

My work day starts at 10am.

If I choose 1hr Service A, then the slots shown to me are correct: 10am, 11am, 12pm, etc.
If I choose 2hr service B or C, the calendar's available slots change to increments of 2 or 3 hours, but they are limited to always starting at the earliest slot:

If I choose 2hr service, the calendar only shows: 10am, 12pm, 2pm, etc.
If I choose 3hr service, the calendar only shows: 10am, 1pm, 5pm etc

This isn't what should happen. I should be able to book a 3hr service starting from 11am, or a 2hour service starting at 3pm. It should allow me to start the service at whatever time, not restrict me. Because another customer could book a 1hr service to fill any gaps.

Am I missing something in the settings somewhere?