Actually, the period of graduation is very subjective. When u perform very well in term of publications, there are some lecturers that would like to squeeze out more from u. I have one friend who have published 10 papers with impact factors ranging from 1 to 5 smth but the lecturer does not want to release him. Now is his 8 semesters and the lecturer keep on saying the results are not enough for phd level. When he referred back to his seniors thesis, it seems that he has 3 times the amount of results presented by his senior