5 CFR § 894.503
Are belated enrollments or changes allowed?
November 4, 2020
(a) The time limit for enrolling or changing your enrollment may be extended up to 3 months after the date you became newly eligible or had a QLE or after the end of an open season. To qualify, you must demonstrate to the Administrator that you were not able to enroll or change your enrollment on time for reasons beyond your control.
(b) If the Administrator allows you to make a belated enrollment or enrollment change, you must enroll or change within 30 days after the Administrator notifies you of its determination.