What she said.
As for time being a dimension, there's a dead easy experiment you can do to prove this. Toss a ball from one hand to the other. It happens fast, right? Now toss that ball *high* from one hand to the other. It takes longer. This is because it has gone through more space. (I know this is blindingly obvious. But sometimes asking 'why?' about blindingly obvious things yields interesting answers). If time was not a dimension inextricably intertwined with physical space, this would not be the case. Space doesn't care if you measure it in millimetres or lightyears. Likewise with time, and hours or aeons.
And yes, I was talking about the M-Theory subset of string theory. Which is weird and peculiar, and upon which my grasp is not sure...
BM