As a theory, I would say it is all in our minds.

I had a experience, medical, my thyroid was killed and the replacement thyroid medication made everything around me stand still. It was my mental state that caused it. I felt no time passing or gravity being the same. I even began to
think everything was fake. I did an experiment to check the
gravity. I did a two mile hike on a very hot day and didn't
get tired or break a sweat. There seemed to be no gravity pull
that should tire you, walking up a hill. For me time was standing still or seem to be.

I think what we perceive as time and gravity is somewhere in our brains. You would think that isn't possible but when I was given the right medication, everything went back to normal. So what ever part of the brain, that that was effected by the wrong hormone, might be how we perceive time.

Gravity and time go together, even if it is just in your mind.