Calculate Hours Ignoring Empty Cells

I am creating a weekly work schedule and want to add hours scheduled for the week. I am able to calculate the hours but having trouble ignorning the days that an employee does not work.
Here's my example of an emplyee that was not scheduled for Sat.
Can someone pls help me with this?



G3 = 11:00 AM
G4 = 3:00 PM
H3 = Blank
H4 = Blank
I3 = 5:00 PM
I4 = 8:00 PM
J3 = total hours for week - difference of G4 and G3 plus difference of I3 and I4