I think I've figured out why time slows down when your high. It's simply because when your high, and more importantly when you're enjoying the high, you are truly in the moment. There is no future, past, but rather a pool of consciousness that is just there and that is the present. When you're high, or when you are in a constant state of "superconsciousness" I.E. advanced practitioners of meditation and yoga, you become aware of the present moment and realize that is all there is. That's why colors are brighter and food taste better, because you can truly "taste" it and you can truly "see" it for the first time. I remember one of the first times I was high I came to the realization that being high is like seeing things for the first time, and it truly is because you are in a higher state of consciousness. Think about it.