The rate at which time passes while lucid dreaming has been shown to be about the same as while waking. However, a 1995 study in Germany indicated that lucid dreaming can also have varied time spans, in which the dreamer can control the length. The study took place during sleep and upon awakening, and required the participants to record their dreams in a log and how long the dreams lasted. In 1985, LaBerge performed a pilot study where lucid dreamers counted out ten seconds while dreaming, signaling the end of counting with a pre-arranged eye signal measured with electrooculogram recording. LaBerge's results were confirmed by German researchers in 2004. The German study, by D. Erlacher and M. Schredl, also studied motor activity and found that deep knee bends took 44% longer to perform while lucid dreaming.

While making the above claim, Hobson et al. incorrectly attribute to me the false statement that "the dreamer can only gain lucidity with its concomitant control of dream events for a few seconds (LaBerge 1990)." [sic.] In fact, lucid dreams as verified in the laboratory by eye-movement signalling last up to 50 minutes in length, with the average being about 2 minutes (LaBerge 1990). The relatively low average is partially due to the fact that subjects were carrying out short experiments and wanted to awaken with full recall. At the onset of lucid dreams there is an increased tendency to awaken, probably due to the fact that lucid dreamers are thinking at that point, which withdraws attention from the dream, causing awakening (LaBerge 1985).

Figure 2. Dream time estimations. We have straightforwardly approached the problem of dream time by asking subjects to estimate ten second intervals (by counting, "one thousand and one, one thousand and two, etc.") during their lucid dreams. Signals marking the beginning and end of the subjective intervals allowed comparison with objective time. In all cases, time estimates during the lucid dreams were very close to the actual time between signals (LaBerge, 1980a, 1985).
It is my opinion that lucid dreams can last HOURS. Considering that LaBerge has a documented lucid dream in the research lab lasting 50 minutes, when most people say a dream can last only 45 minutes should tell you something right there. Some estimates even put it up to around 2 hours. I've had ones that went on for 4 hours, but I may have performed DEILD at some point so it was probably more like 2 or 3 lucids chained together.

But still the point is that, either lucid dreaming is not limited to only REM sleep, or you are able to extend REM sleep while lucid. This is something I've tried to research but haven't found much to explain it.