The deal is good now through Sunday, May 8, 2016, which coincides with Mother's Day (in case you want to order so that mom doesn't have to cook).
As a price comparison, the chain has been offering 2-topping medium pizzas for $5.99 each for a while now, but only when you buy two. A 2-topping large pizza normally goes for $14.49 in my area.
Photo via Domino's.