Schedule overrun is a major problem that disturbed software project team. How to solve this problem? For most software project managers, the first reaction is to work overtime. There is no doubt overtime can alleviate this problem to some extend, but is it an effective way all the time? If not, when shall we give up overtime and change to other ways? This paper analyzed those problems in detail and gave some conclusions in the end. That is for a software project team which has reached its overtime limit, further overtime can only result in much longer completion date. Thus the best overtime policy is to first set a proper scheduled completion date, then try to find the minimums project completion time. The overtime range related to this minimums project completion time will be the critical point to stop further overtime.