Filtering Drop Down Options

I am creating a booking site for rentals. I have a data type called Booking Calendar with the fields (Date, time…etc). When the user clicks on a calendar day, a pop up displays a drop down with available times for that date. How do I make it where the drop down only shows available times for that day? How do I get the site to identify that date and time are already in Booking Calendar and cannot be selected

It would be helpful to have more info/screenshots, but you could try making the popup a data type of Date, and add a workflow when a date is clicked in the calendar to “display data in a group/popup”, setting the popup’s date to the clicked date. The the popup content could reference the parent’s date’s available times. Hopefully that’s helpful.