Here is an explanation of the role of "Time" in a relative co-ordinate system, as a dimension. Whilst it is called "Time", it does not mean "Time" as in the sense of perception, but rather, as a measurement of a physical dimension.

Imagine two cars travelling in the same direction, parallel to each other. Assume Car 1 is travelling at 50Km/h and Car 2 is travelling at 100Km/h.

Now picture a light beam travelling in the same direction as the two vechicles. We will assume the "vacuum speed" of 1,079,252,848.8 km/h.

Now, if the two cars were at rest (stopped) light would pass the cars at a speed of 1,079,252,848.8 km/h.

Simple enough.

Now, if the Car 2 were to pass Car 1 on the road, Car 2 would pass Car 1 at a relative speed of 50 Km/h (100Km/h - 50Km/h).

Again simple enough, now consider this:

If car one was traveling at 50Km/h, light would pass the vechicle at 1,079,252,848.8 km/h and not the 1,079,252,798.8 km/h (light speed - 50Km/h) that would be expected.

In the same way, if car 2 were travelling at 100Km/h, light would still pass by that vechicle at 1,079,252,848.8 km/h and not the 1,079,252,748.8 km/h (light speed -100Km/h) as would be expected.

As Einstein goes on to demonstrate, this is due to "dilations" in the dimension he coined "Time", in a relative co-ordinate system.

So, now consider the implications:

Speed = Distance / Time

As "Distance" is a measurement that uses time, the standard unit of measure will alter. Due to the "dilations" in the dimension of "Time" , it will also alter.

Therefore "speed" would "appear" to alter, when in fact, it remains constant and "distance" alters. Since the "dilations" occur in a dimension known as "Time", and the effect can be measured, it provides emprical evidence of the existence of such a dimension. That is, a concept cannot have "dilations" that can be measured, thus, there must be something to "dilate".

As these "dilations" do not distort the physcial space (think of countless trillions of photons) another "hidden dimension(s)" is required, to warp space and position all the particles. This explains events such as entanglement, VSL, etc.

Its from these understandings that M-Theory, strings, branes, etc., arise. A "hidden" cosmic gap filler.