If the 180th day is Saturday, just wait until Monday. Andre LeGras' disability insurance denial letter said he had 180 days to file an internal appeal. The 180-day period ended on a Saturday. LeGras mailed his appeal the following Monday, and the ERISA plan administrator denied it as untimely.
The 9th Circuit held (2-1) that the appeal was timely. LeGras v. AETNA Life Insurance Co (9th Cir 05/28/2015).
The majority said it had the authority to develop "a body of federal common law governing employee benefit plans." And here is the court's holding:
where the deadline for an internal administrative appeal under an ERISA-governed insurance contract falls on a Saturday, Sunday, or legal holiday, the period continues to run until the next day that is not a Saturday, Sunday, or legal holiday.
The dissent says this is a simple case of contract interpretation, and LeGras was two days late. "The Plan terms are clear and comply in every respect with ERISA regulations," so there was no reason to bail LeGras out.