To quote one of my other posts:

Technically speaking, It's not possible.

Here is a direct quote from Stephan LaBerge's book "Exploring the World of Lucid Dreaming".

Mind/brain/body relationships during dreaming One of the earliest experiments conducted by my research team tested the traditional notion that the experience of dream time is somehow different from time in the waking world. We approached the problem of dream time by asking subjects to make an eye movement signal in their lucid dreams, estimate a ten-second interval (by counting one thousand and one, one thousand and two, etc. ), and then make another eye movement signal. In all cases, we found time estimates made in lucid dreams were within a few seconds of estimates made in the waking state and likewise quite close to the actual time between signals. From this we have concluded that in lucid dreams, estimated dream time is very nearly equal to clock time; that is, it takes just as long to do something in a dream as it does to actually do it.

You may be wondering, then, how you could have a dream that seems to last for years or lifetimes. I believe this effect is achieved in dreams by the same stage trick that causes the illusion of the passage of time in the movies or theater. If, on screen, stage, or dream, we see someone turning out the light as the clock strikes midnight, and after a few moments of darkness, we see him turning off an alarm as the bright morning sun shines through the window, we’ll accept (pretend, without being aware that we are pretending) that many hours have Passed even though we “know” it was only a few seconds.