How to take a half day?

So I’m going to have to leave around lunch time for an interview in a few days. I’m curious how much I will get paid? Since a school day is 6 hours and 30 minutes, do I need to stay exactly for 3 hours and 15 minutes in order to get exactly half my pay, even though some of that would be my lunch and prep?

Assuming I use half a CAR day, will my CAR days now have a “.5” or something next to my full amount, since I only used half a day?

Or will they just put a full CAR day in the system?

I would just call out, but I have a very important meeting in the morning