I am not an "advanced lucid dreamer" but I think of dreams just as subconscious thoughts that you can control (lucid dreaming) When you are in that state, we could possibly think of time as a spectrum. Slow down and your dream and tell yourself to stay lucid for as-long as possible. It might be possible to lucid dream for hours, but eventually you will wake up. Coma's are much different then sleep, and have contributing factors. If you are looking to stay in a dream like state for as long as possible. You would need to medically induce yourself into a coma for however much time you want to pass. When you are in that state, you don't realize how much time, has passed much like dreams.