ELI5 - Is time a real, tangible thing, or just a concept invented by humans that doesn't actually exist?

Also, if time does exist, doesn't there have to be a definable beginning or end? Otherwise it's just infinity which to me suggests the absense of time.

I partially read "The Discoverers" by Daniel Boorstin several years ago and he discussed how different societies conceptualized of time and how they kept time. And it has had me wondering ever since. Then I started exploring Zen Buddhism which emphasizes the present moment as the only tangible reality, along with the illusion of the ego, which only furthered my questioning.

EDIT - I am aware that the concept of time is based on the revolution of the Earth and it's moon. However, that is just how humans conceive of time. That's not proof of time itself.

EDIT 2 - The explanation of timespace and relativity is the best from an objective point of view. No matter how much I read or watch, it was always a bit hard to grasp but it makes sense in terms of change or entropy. The reality of time being flexible vs the human perception of time being linear and unchangeable gets closer to what I am asking.

EDIT 3 - "Exist" is a tricky word.