Subtraction of H:MM

I am trying to set up a timesheet that will automatically add up the hours worked for each day (stop time - start time), then sum up the week and convert it to a decimal (need 4.5 hours vs. 4:30). I have the conversion from H:MM to a decimal, but for some reason the hours are not summing up properly once they go over 24 for a given week. If they are under 24, then the formulas work fine. What am I doing incorrectly?