19 hours
9am, 10am, 11am, 12pm, 1pm, 2pm, 3pm, 4pm, 5pm. 8 hours.
9am, 10am, 11am, 12pm, 1pm, 2pm, 3pm, 4pm, 5pm. 8 hours.
12am to 4pm is 16 hours.
6 hours from 4pm to 10pm
22
7am to 4pm is 9 hours.
It is 12 hours from 4pm to 4am.
4pm
4pm to midnight is 8 hours.
72
10am to 4pm is a period of six hours.