It's not necessary to have multiple services when you have multiple durations.
For example, DON'T DO THIS:
Rather, Bookem allows you to add different durations for the "same" service - see the example below, Follow-up Consultation - with duration options of 30 minutes, 45 minutes or 1 hour.
To do this, when adding or editing a service, simply select the "+" and add the next duration, that way your client can select the time from the drop-down that will appear on the public booking page.
Also, each Location can have different durations and prices.