course durations

Hello we have this issue that we just found out today scenario : We have 9 courses that's has 45days each duration and each courses is prerequisite for example course 2 cannot be start if the course 1 is not completed/finish. so our issue is we manually assign all 9 courses to the students and technically we found out that all courses already automatically start the countdown / duration without the student actually start the course. for example we assign the student all the course March 5 so originally the student has 45 days to finish the course 1 , however the student haven't done anything and the student told us today when he login he ask why the duration already use and now he has 40 days to all courses even thou he is not doing anything. Hope you could help us out how to solve the issue. and hoping you understand our issue. we are using WPLMS 3.9XXXX version thanks thanks