Enrolment

Hi! My problem is that I want to enroll students same course but with different limitations, for example: 1. 1 month access for 1 registered user to the course on training portal, ie for given time span only. 2. Course availability time begins once user registers and begins course. 3. 1 year of unlimited number of user access to course. What I understand is that all the enrollment restrictions available are for the courses, not for the student. If we define "1 month access for users, course availability time begins once user registers and begins course" this rule will imply on each student enrolled to that course. But I want some people to have access for 1month on a course and some have 1year on same course. I’ll appreciate if some one gets me out of this puzzle  Thanks in advance.