Remember the pay is what is called in arrears. IOWs the 15th paycheck would be for the 1st-15th. Thus, if you don't contract until the 7th than you will not get the full amount for that pay period on the 15th. Same with the end of the year. If school ends on May 10th, than on the 15th that pay will only be for 10 days, not 15.