Quantity of Service

My business offers the same service in different time increments. Is there a way the customer can choose the time/quantity of the booking without having to add a whole new service albeit just double the time. 

The reason it is a problem is because we have the same service for different rooms. so depending on the room type and service duration I am going to have to have a very long list of options. We will also soon have two locations so that will double the amount of services available. 

We also offer the option for customers to choose their staff member, I cant see a way that i can have the same service with the option to which room, all within the same calendar. 

Help please!