Seven and a half hours.
8
8 hours.
Nine and a half hours.
840
Nine hours.
4.5 hours
1345
9.5
ten and a half
8:30am to noon is 3.5 hours.
It is (8.5 + 24k) hours where k is an integer.
8 hours and 30 minutes.
4:30am to 4:00pm is 11.5 hours (11 hours 30 minutes)