(1) Any interested person who can and will provide all or any part of the proposed service may file a protest against the application. Such protest must be specific as to the service which such protestant can and will offer and must consist of a signed original which must be filed with the commission in Helena, Montana within 15 calendar days after the service date shown on the notice. One copy of such protest must be served on the applicant or its authorized representative, if any, by U.S. mail or in person. Thereafter the commission may grant temporary authority with extensions, but in no case shall a grant of temporary authority exceed an aggregate of 120 days.