So we can only measure the effects but not the laws themselves.
We know gravity exists on the basis of its effects - how it manifests on the behaviour of objects.
In fact there are vast numbers of things that we determine to exist on the basis of their measurable impact on our world.
That still doesn't explain how they are not dependent on their existence on time and space.
Time and space are measurable consequences of those physical laws, just as the measurable and predictable orbits of the planet in our solar system are a consequence of gravity as a physical law.
In what way can they said to exist apart from time and space then?
I didn't say they could - it was you who implied that time/space and physical laws were independent on each other. I on the other hand clearly stated their dependency - in other words that time/space time are manifestations of those physical laws - time and space only exist because of those physical laws.