How to make a drop down list of times?

Question

PHP

In one company there is a conference room, so that one conference does not occupy another, the heads of the department plan them about a week in advance, choose the date and time, and the time is not from to, but by 1 hour, that is, if they choose 10:00, it means that from 10 to 11, here I took the script https://htmlweb.ru/java/example/calendar.php to select the date , now we need to do the same for the time, and the busy time should be painted red, the entire schedule is stored in mysql