We're staying in a hostel in Purmurarca tonight (hostel being a flexible term since the room is nicer than most 3-star hotels). The town consists mostly of 4 square blocks, and its economy appears to depend largely on tourism (the center being filled with tour buses and "artisanal" street vendors during the day). It's no longer peak tourism season (judging by the availability of lodging) and at 6pm the vendors were packing up. There were still a good number of foreigners walking around looking for dinner, however, but nothing was open.
Around 7, we passed a restaurant in the center of town with tables cearly set up for dinner, but it didn't open until 8. We met a Dutch couple on the same quest for dinner. They noted positively that the place looked fancy.
We kept walking, and having traversed the whole town, were about to give up and cook pasta on the camping stove, when we found one open restaurant. The waiters weren't on duty yet, and a tv on the wall was playing a bad American movie dubbed in Spanish, but the menu had what we wanted, so we ordered.
Between 7:30 and 8, the waiters arrived, the movie was replaced with dinner music, and everyone we had seen walking around (including the Dutch couple) wandered in. The food was good, and by the time we left, most of the tables were taken.
Out of curiosity, on the way back to the hostel we passed by the fancier-looking place that opened at 8 - and it was completely empty, in an empty square. They had missed their entire business for the night by opening half an hour too late.