How can we limit how many times someone can select pre-set available time from dropdown?

For example i would want to limit the number of selections/form submissions for a drop down list. 

Example: 

930am-1030am - limit to 15 clicks

1030-1130am - limit to 15 clicks

Total of 60 clicks only and form will be closed for submissions. 

Based on what you have mentioned there are 2 things.

1. You want to separate the the number of selections of specific time

2. You want to limit the number of submissions on your jotform.

To accomplish the first, I would suggest using our Appointment Slots widget.

You can see here how to add it: How to Add a Widget to your Form

Now in regards to the second question, I would suggest taking a look at the following guide: How to Limit Submissions in a Form

Do let us know if you have any further questions.

Now I should just mention that usually we can assist with only one question per thread, but as they are both short, I have answered both here.