13
21 hours
It's 7 hours 4pm = 1600 9 am = 0900 16 - 9 = 7
9am, 10am, 11am, 12pm, 1pm, 2pm, 3pm, 4pm, 5pm. 8 hours.
(7 + 24k) hours where k is an integer - likely to be 0.
MON-FRI: 9am - 5pm / SAT - SUN: 10am - 4pm
MON-FRI: 9am - 5pm / SAT - SUN: 10am - 4pm
MON-FRI: 9am - 5pm / SAT - SUN: 10am - 4pm
MON-FRI: 9am - 5pm SAT - SUN: 10am - 4pm
MON-FRI: 9am - 5pm / SAT - SUN: 10am - 4pm
MON-FRI: 9am - 5pm / SAT - SUN: 10am - 4pm
12am to 4pm is 16 hours.