The semestral calendar being used by PLM consists of two regular semesters of about 15 to 16 weeks each , and semestral breaks of about three to four weeks each . Except from the graduate schools of Engineering , Law and Management , which have trimestral calendar , most of the colleges and schools of PLM consist of two regular semesters of about 15 to 16 weeks each , and semestral breaks of about three to four weeks .