N.D. Admin. Code § 81-09-02-04 — Due dates for filing a return and paying tax

If the due date for filing a return and paying the tax owed falls on a Saturday, Sunday, or legal holiday, the return and payment are due on the next business day. If a taxpayer is required to file an amended return, this return is due on the date set by the commissioner. A return is delinquent if it is postmarked or transmitted after the due date. A payment is delinquent if it is postmarked, or an electronic payment is initiated, after the due date.