Ever notice during the summer the hottest part of the day is usually around 3 or 4 in the afternoon instead of at noon? Same thing, just on the order of months instead of a day.
It's a timezones vs actual sun time thing. In Spain near me they are like 2 hours away from their actual sun time so you can even add that to the lag you said. I'm sure it's the other way around somewhere in the world, specially in medium and big countries
That's the thing though. Spain's time zone is so far ahead of where it should be, for most of the year the hottest part of the day really is around noon. When stupid-pretendy-time is in effect (which a quick google tells me is 7 months of the year), solar noon is at 10 am in Spain, which means clock noon is at 2 pm, roughly the hottest part of the day.
There's also the fact that local factors have an effect. Closer to the equator, the hottest part of the day tends to be earlier. Humidity can have an effect, as can the amount of concrete and asphalt versus earth and trees.
I spent about a week in Toledo, Spain for a wedding a few years ago during the summer. We were taking siestas on our second day there and eating dinner at 10pm.
It was actually quite enjoyable operating on the Spanish time-conventions.
The thing is, the time zones aren't necessarily related to the lifestyle. A siesta at 1 on the current clock is identical to a siesta at 11 on a more natural clock. But either way you have a siesta when the sun is near its peak.