My friends in the pizza shop business tell me those two nights would be about half the week's revenue and the majority of profit if the other five days are used for intensive prep work and administration.
That's probably true; opening 6 or 7 nights a week would certainly not triple their business. It would, however, give them a lot more open-time to accumulate repeat customers. Whether or not that works out in their favor in the end depends on how leanly they can run on those slow nights.
Assuming that the two nights they currently open are on the weekend, perhaps opening for the remainder of the week wouldn't triple their business, but there's probably relatively predictable demand for pizza on weeknights, and I'd assume they could do/have done the research to determine whether, given that demand, they'd make a positive ROI by opening seven days a week.
