When we first arrived in Spain shopping times, were, pretty much, regulated. Shops, except maybe bakers and paper shops, didn't open on Sundays and The Sales only took place in July and after Kings in January. There were lots of rules about how long they had to last, how the discounts had to relate to the prices on goods which had been available in the shops for weeks beforehand and all sorts of other stuff. Nowadays shops can have Sales whenever they want. But custom and habit are culturally powerful and people still think of, and wait for, the Summer and January Sales
The rules were relaxed in 2013. As well as the changes to The Sales there were lots of changes to the opening hours of shops. For example, weekly opening hours were increased from 72 to 90 hours for shops over 300 square metres, which explains why none of the big supermarkets are open 24 hours, but why there is a boom in the smaller town centre supermarkets. Shops under 150 square metres can open when and as they please - on Sundays, on holidays, 24 hours a day. It's not easy to generalise about the legislation, and I may have some of this wrong because it is all ifs and buts because the Central Government rules can be varied by local rules from the Autonomous Communities. For instance before the changes shops could open 12 times a year on Sundays and holidays but the Regions could reduce that to eight times per year. Now the National limit is sixteen times (for the bigger shops) but the Regions can reduce that to as few as ten times per year if they wish. The National legislation also allowed big shops in important tourist destinations, determined by the figure for overnight stays or the number of cruise ship passengers, to open all year round. That's why, for instance, Cartagena has a lot of Sunday shopping but Murcia city doesn't.
In the area we live, in Valencia, local legislation sets the number of Sunday and holiday openings for big stores to eleven times per year but it also gives "special status" to some areas, the ones with most tourists, like Alborache, L'Alfàs del Pi, Finestrat, Torrevieja y la costa de Benissa, Orihuela y Pilar de la Horadada where the shops can (I think) also open the additional Sundays, and any holidays, between mid June and mid September. The big shops and shopping centres outside those areas - in Alicante and Valencia cities in particular - don't get that extra summer dispensation and the eleven possible days they can open do not include the traditional Sundays on which the Summer and January Sales start, two of the busiest days of the year. So those big shops and centres feel hard done by and have taken the Valencian Government to court to make it comply with Central Government legislation. Of course it takes years for some legal actions to get to court so, in the meantime, the local legislation holds good.
Even if you found that confusing it may explain why some of the "Chinese" shops seem to be open all the time, why big supermarkets aren't and why lots of shops are open on the run up to Christmas.
