Trying to figure out how to calculate hours on a schedule using excel

Hi I’m trying to work on a schedule and have everyone listed as like ANON 9-5 or 9-4 in a chart and I’m trying to figure out how to set excel to calculate that “9-5” is an 8 hr shift and put it off to the side of the calendar so I can keep track of hours used without doing it by hand. I looked into conditional formatting but it just keeps trying to change the colors of the cells instead of calculating anything for me. Any help is appreciated thanks!