Hey there @Labrina111122 - great question! Check out our New User Guide and our Company Admin Guide as you learn your way around Calendly. They are both super helpful resources! 

As it pertains to your question - at this time there is no way to set up multiple durations under a single event type for invitees to select from when booking. I am sorry about that!

A work around we’ve seen many users successfully implement is the creation of multiple identical event types with different durations to choose from. So, you can clone one event type multiple times and simply change the duration, leaving all of the other settings as is. 

Then, you can implement routing forms so that an invitee is asked a simple question (such as “How long would you like to meet?” with answers to choose from like, “30 minutes” “60 minutes” and “90 minutes”) and is then routed to the event type that lines up with the right duration. 

Routing forms let you request information such as industry, company size, specific interests, etc. from website visitors and automatically direct them to a specific scheduling or web page based on their responses. It's great for screening and qualifying sales leads on a website or matching clients or students to the booking page of the right subject-matter expert based on their interests, program, or other criteria. You can read more about setting up routing forms, here!

I know this isn't exactly what you wanted to hear but do hope the information helps, at least somewhat!