How much happens in a single second?

Quite a lot actually.

How much happens in a year?

Well, 3.154e+7 times what happens in a second, as that's how many seconds are in a year.

So, what marker do we actually have that indicates a second has gone by?

Is it... nothing? Just whatever arbitrary number we thought fits a second well?

Or is it actually a derivation of how long a year is?

That means our "unit" for time isn't the second, the minute, the hour, or the day.

Our measure for time is whatever orbital pattern our entire existence is currently set upon.

In other words, the de-facto unit of time is however long it takes for the Milky Way Galaxy to make one trip around the center of the Universe.

Well, that's nice and dandy, but how many seconds is that?

Oh, what's this? It's relative to how close you are to the orbital body? Theory of Relativity, you say?

Uh oh, what's this?

https://blog.drwile.com/the-axis-of-evil-in-astrophysics/

Axis of Evil, aye? You're telling me that the plane that the orbital path the Earth takes around our Sun is the origin of the Universe's perceivable microwave background radiation? and that implies that the Midpoint between the Earth and the Sun is the center of the Universe?

Interesting... And if time is relative to the most massive "cycle."

Does that mean the Sun-Earth plane is effectively the only location to find the fastest period of time?

Well, that sure does make our little rock in space a ton more significant as it pertains to space-time, aye?