41 C.F.R. § 301-11.13

(a) Employees will generally be reimbursed for subsistence expenses during non-workdays (weekends, Federal holidays, or other scheduled non-workdays) when their travel status requires staying at the temporary duty location or traveling during these days. However, the agency should determine the most cost-effective approach, such as remaining in travel status or permitting return to the official station.

(b) For emergency travel due to incapacitating illness or injury, the rules in part 301-30 of this subchapter apply.