Calendar tool by Brown Fox

Can anyone help me with this?

What I have in mind. Build a list of dates (rg with all the dates of the current month, and I think I got it).
After that, when the user clicks on the day (the 21st as in the image above) another rg should show the list of available times for that day. Like, the registered establishment works from 8:00 am to 6:30 pm, the customer will select a time between that, then he will check if it has not already been booked by another customer, if not, an appointment will be scheduled. So I want to show only cells within that range 08:30 to 18:30. However, it is showing all the hours of that day with the plugin’s default interval (60 min) which I will later change and make dynamic.

Can someone help me with an example maybe. I’ve been on this for days.

Actually the time interval is 20 minutes in the image above.