Ok, so it isn't quite as large, but I had to shorten it a bit as I'm writing this from work and I'm a little given to hyperbole. Otherwise I'd also include some of the deranged theories that I've come up with after a long day of getting a high off caffeine and being up at 6 in the morning.

The first three dimensions are partially based on the fourth, but only in movement not in existence. If time were to freeze at this very second all of the first three would still exist, yet there would be no movement through them. From this simple fact (or something closely related) we were able to come up with rate.

Rate is determined by the speed at which an object's place in the first three dimensions changes between two points in time. These distances can be measured in several different ways, using systems such as the metric and standard. The times may also be different, but usually they are hours (unless you are an astronomer, where the main distance is a light year and the time is a second).

The reason I say that time's rate is constant is because according to Einstein's Theory of Relativity time is relative to the observer, and the observer observes time at a constant rate. Thus making time constant. I have no doubt that we will soon be able to more accurately study time and its properties later on, possibly even leading to travel between two points on this fourth dimension.