Opening hours
Shops, restaurants and offices open at seemingly odd times. It is actually hard to say when they open and close.
As a rule of thumb -with many exceptions to this rule!- count on shops to be open between 10 am and 2 pm and between 4 pm and 8 pm. Indeed, the siesta! Banks usually close at 2 pm, to not open again that day.
On Sunday all shops and offices are closed - no exceptions, except for the market in Villaricos, of course.

Restaurants may or may not be open during the siesta for lunch. In general they'll close at a somewhat nondescript time: 'at closing'. So if you're the last guest, you basically decide what time that is. In any case the kitchens typically close at 10:30 - 11 pm.
Spain is / was a foremost catholic country, meaning there are many fiestas and holidays, many of which are so called 'red days'. In addition, the various regions or communities have their own holidays to commemorate an historical or political event. Count on everything to be closed on those days.
To avoid disappointments, it is best to search the internet for upcoming holidays in the region you intend to visit. Or, in your best Spanish, ask one of the locals.