Help with Schedule formula

I am trying to create a spreadsheet to keep track of my employees hours and having a difficult time doing so. I have the employees listed A2-A6, and the hours B2-M2, C3-M3...and so on for 5 employees. I am trying to calculate the weeks total in N2 through N6. I have each day cell formatted to 1:30, and the total for the week cell formatted 13:30, but it will only calculate Mon-Wed, then the total number of hours goes wrong starting with Thursday. The formula I have started is =SUM(C2-B2)+(E2-D2)+(G2-F2), but when I enter (H2-I2) it messes up!!! What can I do to correct this?