not in real time but in dream time, i have seen that some of
you speak like you have been in a dream for days… i can’t even
imagine that, i mostly wake up after minuts if not seconds wen i
become lucid
…
Most of my LD’s are just some minutes, but some have been several hours long 
But its not the length that matters, its the Quality 
My longest one was also my most recent one, and it felt like about half an hour, maybe a little more, it’s a little hard to say with dreams. That was the dream where I didn’t do much other than just explore my surroundings, with minimum manipulation, and I still had to work hard to keep the world stable.
My earlier lucid dreams have been just a few minutes long. It takes practice.
The can last anytime really, in dream time of course the only thing that defines the time is your body clock and what you see. In a dream these are both simulated so it can last a second or a day or a week or a month or a year or even a lifetime.
Yeah - you’re right 
My last LD was very long. About half day… but, unfortunately I thought I couldn’t wake up (silly, huh ? 
) and I made myself to wake up - I can tell, I could have enjoyed another half of the LD 
But LD’s can vary between seconds and months (or even years) - it requires experience and a lot of practice. The mind cuts of very many parts of the dream to make it feel like days, when in fact you enjoy only 2 hours or so of your REM.
So, time in dreams is completely different… sometimes
I rarely think about how much time passes me by as I dream. Mostly my dreams are several scenarios or stories stringed together to form one entire dream sequence, so it never feels like I spend more than a maximum of a few days in a drem scenario. It’s not until afterward when I tell my friends about it and they go, “Wow, what a long dream you had…” that I realize that it was pretty long and detailed. I think my record is six months in a dream, though - but I had several timeskips. It never felt as though I spent more than a couple of days in one place.
I have had those who feels like hours or almost an entire day. The usual is 1-10 minutes i guess, very varying.
Mine last a few hours or almost a whole day, I rarely get LD’s that exceed a day 
Usually, between 5 to 15 mn, but it tends to fall at the moment 
I have to practice my concentration! 
Soon I will be very lucid