Booking with different durations

For a Computer store we need to have the possibility to have the client choose a service for appointment.
The available options would be:
A. Information/Purchase of a new laptop/smartphone/tablet (in-store) (30 min)
B. Information/Purchase of a new custom (gaming) computer (in-store) (45 min)
C. Information/Purchase of hardware/software (in-store) (30 min)
D. Information/Purchase of network/Wi-Fi (in-store) (35 min)
E. Order pickup (in-store) (15 min)
F. Technical support (on-site) (60 min)
G. Technical support (remote – SOS ComputerStore) (30 min)

I tried to manage this with different Bookings (Apps) and also with 'Options' and different services , but we that doesn't prevent the double bookings in the Calendar of course.

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