Mont. Code Ann. § 25-31-705

The trial may be postponed upon the application of either party for a period not exceeding 4 months. The party making the application shall prove, by the party's own oath or otherwise, that the party cannot, for want of material testimony that the party expects to procure, safely proceed to trial and shall show in what respect the testimony expected is material and that the party has used due diligence to procure the testimony and has been unable to do so.