Wow. Just found this thread. I just posted a new one in the wrong place (Pathways to Lucidity) about the same question. Ooops! Mods, move or merge or whatever…[What's the longest lucid dream you ever had?)
But I don’t understand claims about LDs that last more than a few hours. I’m wondering about time as it occurs in waking live…ie the Sun rising and setting. I know time is wacko in dreams and it can seem like a long or short time and upon waking you are surprised to find it doesn’t synchronize.
But we only have a limited amout of REM each night as adult dreamers, and even if you can manage to jump back into your current LD when one of the REM sequences ends and then begins agian (not easy for me), that would still only be a few hour total for that one sleep cycle.
I suppose there could be those who can dream in a serial fashion, like some neverending script that picks up where it left off each night. But I was primarily interested in maintaining the Lucid state and making it persist. Not neccessarily being able to regain it across multiple sleep cycles.
probably about 15 to 20 minutes. it was the best LD i’ve ever had 
As for me, I’ve had about 6 LD’s which lasted around 20 to 30 minutes. The longest LD recorded in laboratory by LaBerge was a full REM phase, i.e. 50 minutes.
No one can know how much his dreams last, cause you cannot always remember the whole dream, and the time in the dream is much different than the real time.
I remember having a dream (not a LD though) about two years back that seemed to last a full year. I was in some strange city for a year and afterwards i had the feeling that an actual year had passed, but when i really thought about all i could remember, i only got together about a few minutes of stuff. I think it is pretty easy to create the illusion of time inside a LD, but to have a dream actually last longer than the REM phase, you’d have to pick the LD up the next night and the night after that and so on.
I think the longest LD I had lasted an hour or so dream time. I’m not really sure if it was one dream or just a series of dreams that continued off of eachother and I stayed lucid through the REM cycles. Each part of it took place in different parts in my house and I have lapses in my memory of going to different rooms.
I actually had a pretty long ND last night. I can’t really remember any details about what happend over the course of the days, but there was this thing where people had to vote on a new species of fish to be invented and once a day one of the fish got eliminated. There was this huge tank full of dozens of fish to be chosen (it’s hard to explain) so I’m assuming days passed, but I can’t remember very much of the days other than being in the room with the tank. I do remember going home a couple of times and getting really close to becoming lucid, but I never did a RC and must have just gotten used to the differences in my house. I can’t remember which fish ended up getting chosen. 
I think that we just don’t remember parts of dreams that are uneventful, or our mind just skips over anything that’s boring to something more exciting.
The longest LD I had was about twenty minutes long.
It was rather fuzzy at the beginning, but most of it was with me stabilizing the dream lol.
I remember walking into the snow in my bare feet and socks and it felt like I was stepping on damp, warm cotton.
about 4 hours a couple nights ago… it was absolutely amazing.
The longest lucid dream I ever had was about a week. I was, let’s say, in the “days of creation” 