Mont. Code Ann. § 25-1-301

Subject to Rule 6(b), M.R.Civ.P., whenever this code requires or allows an act to be done at or within a specified time, which act relates to the pleadings in the action, the undertakings to be filed, the justification of sureties, the preparation of statements or of amendments thereto, or the service of notices other than of appeal, the time allowed by this code may be extended, upon good cause shown, by the court in which the action is pending or a judge thereof; but such extension shall not exceed 90 days without the consent of the adverse party.