Einstein actually admitted to not knowing what Time is, but conjectured that it was probably “man-made”….he may have meant abstract.
Interesting how he formed a theory founded on Time (spacetime), when not knowing precisely what Time is.
You try putting forward a theory based on a vague, ill-defined noun, and see how far you get.
And Physics still hasn’t defined or understood Time since. That is a big black hole…
What is Time? 