42 CFR §407.12

1. (a)Opportunity to enroll.
   1. (1)An individual who is eligible to enroll for SMI may do so during an initial enrollment period or a general enrollment period as specified in §§ 407.14, and 407.15. An individual who meets the conditions specified in § 407.20 may enroll during a special enrollment period, as provided in that section.
   2. (2)An individual who fails to enroll during his or her initial enrollment period or whose enrollment has been terminated may enroll or reenroll during a general enrollment period, or, if he or she meets the specified conditions, during a special enrollment period.
2. (b)Enrollment periods ending on a nonworkday.
   1. (1)If an enrollment period ends on a Federal nonworkday, that period is automatically extended to the next succeeding workday.
   2. (2)A Federal nonworkday is any Saturday, Sunday, or Federal legal holiday or a day that is declared by statute or executive order to be a day on which Federal employees are not required to work.