This is a timesheet:

A1 B1 C1 D1 E1 F1
Time 9:00 am 12:00 pm 9:00 am 12:00 pm OFF
Total 3 3 #Value!

I have time in and time out with total hours caculating. The formula I am
using for total hours is a simple C1-B1 with HH:MM format.

I need to enter OFF, SICK, OUT for days that the employee is not in but I
get an error value. How can I make it so that the formula adds the hours
entered and ignores any other values such as OFF, SICK, OUT.