edx課程的開課時間，註冊時間

lms/djangoapps/courseware/access.py(164)

now = datetime.now(UTC())
enrollment_start = course.enrollment_start 
enrollment_end = course.enrollment_end

common/djangoapps/course_common/views.py(1533)
course = modulestore().get_course(SlashSeparatedCourseKey.from_deprecated_string(course_id), depth=0)
course_start = course.start.strftime('%Y-%m-%d %H:%M:%S'),
course_end  = course.end.strftime('%Y-%m-%d %H:%M:%S'),