Three problems jump out at me.
#1 - By being salaried, they can be pushed to work more than 30 hours. (say 40 hours).
#2 - The core hours that everyone on the team is there is 10-2. That's 3 hours assuming people take lunch.
#3 - It's assumed people with a shorter week want to work Monday - Thursday. Some might want to work a shorter day on all five days to assist with childcare.