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 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.
Each duration can be priced differently, or have different pricing item(s) associated.
Also, different Locations can have different durations, prices and/or pricing items to each other.