Technically time cannot be a dimension like length, width, and height because it is relative. With length, a meter is a meter is a meter. Obviously a meter is an arbitrary comparison to some rod held at some constant temperature somewhere, but the length will never change.

Time is NOT like this. We, as people one earth, could be instantaneously frozen for millions of years, come out of our freeze instantaneously and it would seem like nothing ever happened. If someone had started a stop watch before the freeze it would not read that millions of years had passed, it would continue counting where from where it was when in froze. The person holding it would be unable to discern that anything out of the ordinary had occurred, but to someone not on earth millions of years would have passed.

TL;DR Time is relative (duh) which is weird and makes it so it can't be considered a "dimension"