Generate dynamic time slot using php mysql

I am building an event based website where I need to display dynamic time slot for the attendees.

During the event every hour has 20 minutes slot where at most 30 people can do some activities. So for example - at 9:00 30 people can do their activities. Then at 9:20 other 30 people can do their activities.

This way it the activities will be running from 9 am to 5 pm for 3 days.

So when someone wants to attend to a specific time slot, the UI will populate all the available time slots counting the database table. If no slots available he will not be able to attend the event and the slot non availability message will be displayed.

I have to build this solution using PHP, MySQL.

Any suggestion will be appreciated.

via Chebli Mohamed