How can we set an Enrollment Duration for students entering a course without an end date?

For example, students access the course, which activates their enrollment in the course, and sets an expiry date when the individual student’s enrollment expires (e.g., 45 days).

Our goal is to offer courses that are essentially open-entry and open-exit once a course is launched. Each student entering the course has an enrollment duration of 45 days. The student is automatically unenrolled in the course, or their enrollment is deactivated when their enrollment expires.