How to set a specific time slot duration in Appoitnment?

https://www.jotform.com/232785335179163

I need to allow a max of clients to register for 3 hour workshops. Please advice. My URL is listed above.

To clarify, I am offering a 3 hour workshop, for example on May 18 for max
of 20 people. How do set you the time of 9:30am- 12:30am to 20 clients to
register for the same time slot?
...

Hi Dr. Cynthia,

Thanks for reaching out to Jotform Support. You can set the appointment duration to 180 minutes. Let me show you how:

1. In Form Builder, click your Appointment's Gear icon to open its properties.
2. Go to the Availability tab .
3. Set the duration to custom 180 minutes. Also, set the interval to 9:30 to 12:30 pm to prevent other time slots from being displayed. 
4. After that, go to the Advanced tab and set the maximum number of attendees to 20. 

Give it a try and let us know if you have any other questions.

Great. I have another question for you. I also want to offer appointments
in 1-3 hour blocks throughout the week; for example Monday @9-10 or 9-12
can I; if so how?
...

My apologies for any confusion… to clarify
I offer sessions Mon- Thursdays in 1-3 hour blocks and on Friday and
Saturday only 3 hour blocks; how do I set that up - max of 20 clients
...

Hi Cynthia,

Thanks for getting back to us. I’m sorry you're having difficulties with this. I cloned your form, and saw that you've already added intervals for Monday to Thursday, and the only thing left is to set up two different appointment durations. Although, we don't have the option to have two different appointment durations, as a workaround, we can add another Appointment widget for the second appointment duration, and then set up a condition to let the user choose between those two. I applied the said changes to the cloned version. Check out the screencast below:

As you can see, the user can select between 1 hour, and 3 hours of appointment duration. You can clone my demo form to make things easier, or you can do it on your own. Let me show you how to do it:

First, let's add the needed widgets for the condition:

1. In Form Builder, hover your mouse over your Appointment widget, and right-click on your mouse.
2. Click on Duplicate.

3. Set 60 minutes duration on the first Appointment widget, and then, set 180 minutes duration on your second Appointment widget.

4. Click on Add Form Element on the left side of the page, and drag, and drop Single Choice widget on your form.

5. Change the label, and the options of your Single Choice widget.

Now, let's setup a condition for your Single Choice widget:

1. Click on Settings in the orange navigation bar at the top of the screen, and in the menu that opens on the left side of the page, click on Conditions.
2. Click on Show/Hide Field.

3. Copy the condition settings below:

4. Click on Add Condition, and repeat the same steps for your second option.

That's it. Let us know if you have any other questions.