I am trying to build a form that will allow another user to enter a DateTime for an appointment. Once the time is picked, i want it reserved in a schedule. 

My problem is: After user A picks monday 9am to 10am, i don't want user B to be able to pick times between that timeframe. I want to avoid all overlaps.

Also, is it possible to change the precision of the Date-Time field? I dont need to pick "december 3rd at 9:52.54".