When by these rules or by a notice given thereunder or by order of court an act is required or allowed to be done at or within a specified time, the court for good cause shown may, at any time, in its discretion (1) with or without notice, order the period enlarged if a request therefor is made before the expiration of the period originally prescribed or extended by a previous order or (2) upon motion made and notice after the expiration of the specified period, permit the act to be done when the failure to act was the result of excusable neglect; but it may not, except as provided by statute or elsewhere in these rules, extend the time for making a motion for new trial, for taking an appeal, or for making a motion for a judgment of acquittal.