The motion for a new trial stating the grounds thereof shall be served and filed not later than ten days after the notice of entry of the judgment.
The court shall make and file the order granting or denying such new trial within twenty days after the service and filing of such motion, unless for good cause shown, the court files an order within said twenty days extending the time for entering such order. If a motion for new trial has not been determined by the court and no order has been entered by the court extending the time for such ruling within twenty days from the date of service and filing of such motion, it shall be deemed denied.
SDCL 15-6-59(b)