If an open end consumer credit plan provides a time period within which an obligor may repay any portion of the credit extended without incurring an additional finance charge, such additional finance charge may not be imposed with respect to such portion of the credit extended for the billing cycle of which such period is a part unless a statement which includes the amount upon which the finance charge for that period is based was mailed at least fourteen days prior to the date specified in the statement by which payment must be made in order to avoid imposition of that finance charge.
Subsection (a) of this section does not apply in any case where a creditor has been prevented, delayed, or hindered in making timely mailing or delivery of such periodic statement within the time period specified in such subsection because of an act of God, war, natural disaster, strike, or other excusable or justifiable cause, as determined under regulations of the Board.