Hello Lisa,

Thank you for reaching out to us.

All time slots are predefined, based on the service duration. There's no option for customers to choose the duration. 

However, there are two options that work for some use-cases. You can make different services, for example, '1-hour service', '3-hour service' and so on. 

The other option is to make one service and add Extras to it, you can make '30 minutes Extras', '1-hour Extras', and so on so that a customer can add them when booking an appointment. Extras are adding duration to the appointment, but you can also define the price and the quantity for extra if you want.

For example, I am the customer and I am choosing the service that lasts an hour, I am adding 3 x Extras of 30 minutes and I am actually booking the appointment that lasts 2.5h.

Hope this helps and let me know if you have other questions.