function llms_is_post_restricted_by_time_period( $post_id, $user_id = null ) {

	$post_type = get_post_type( $post_id );

	switch ( $post_type ) {
		// If we're on a lesson, get course information.
		case 'lesson':
			$lesson    = new LLMS_Lesson( $post_id );
			$course_id = $lesson->get( 'parent_course' );
			break;
		case 'llms_quiz':
			$quiz      = llms_get_post( $post_id );
			$lesson_id = $quiz->get( 'lesson_id' );
			if ( ! $lesson_id ) {
				return false;
			}
			$lesson = llms_get_post( $lesson_id );
			if ( ! $lesson_id ) {
				return false;
			}
			$course_id = $lesson->get( 'parent_course' );
			break;
		case 'course':
			$course_id = $post_id;
			break;
		default: // Don't pass other post types.
			return false;
	}

	$course = new LLMS_Course( $course_id );

	return $course->is_open() ? false : $course_id;

}