> I might describe it more as "flow" where work gets done and you look at the time and 4 hours have passed.

In my mind, zen goes deeper than flow. Flow is just the vegetable brain part of it. With zen, it also feels like I'm doing my own mental state some good by just being myself at the same time.
At least that's how I draw the line between those two. I reserve the right to be completely wrong.

unboiled

I might describe it more as "flow" where work gets done and you look at the time and 4 hours have passed. The last time I remember was years ago composing music. Nowadays it happens on occasion when I get really into something like pulling weeds in the garden or digging in the sand.