It's wild to think about how different things were in pre-modern times.

There are no computers, sensors, watches, or spaceships. There are also no TV-style distractions, and a lot more people are growing food. When would you notice that the longest day of the year is a few days away from what the books say it's supposed to be?

For that matter, the printing press was only a century old. How well-known was it that particular days are meant to be the longest or shortest of the year?

In an agrarian economy people are definitely much MORE attuned to the cycles of the seasons. If your town always starts planting crop X two weeks before the solstice, and the harvest festival is the week after the equinox, you’re going to keep track of these things.

If I recall correctly - it was surprisingly well known (in fact it was a common way to make fun of "lettered" people because they'd claim dates that were obviously silly; everyone knew when the solstice was).

Some of the earliest things we have a sun-based calendar trackers, which need not be more complicated than a stick and a rock (meaning millions more have not survived).