Shops and restaurants, and many petrol stations, seem to close for lunch in Spain. Which is fine if you can plan for it, but having been stuck, with the family, in a car in 35°C temperatures for over an hour waiting for a petrol station to open (hoping it would open, as there was no sign showroom opening hours) I was wondering if there was any standard set of hours for siesta?
There is no written rule about "siesta" time. Usually the siesta starts after lunch and ends one or two hours later. It is a wrong idea to think that most Spanish have a siesta time, it happened some decades ago, but today is not a generalized practice.
Anyway, you have to difference between siesta time and business timetables. Probably Spanish timetables are influenced by siesta tradition, but you have to take into account other elements like the high temperatures we have in summer or the big meal we take around 2 o'clock.
Given this, you have to worry from 13:30 to 17:30. These 4 hours are the most problematic, but I don't know any petrol station closed on this hours (in fact most petrol stations are open 24 hours a day), restaurants usually close at 4pm except in touristic areas where the restaurants adapt their schedules to the tourists they receive. General shops may be closed on this hours but the malls remain open.