Some time back, I had a lucid dream that felt like it was around 25-45 minutes long (the range is so wide because it's hard to estimate time passage in dreams--the best I can do is go through the events I remembered and try to guess how long each one took). Before that, the longest ones were maybe around 5 minutes or so, so that one was quite impressive.

Lately, the majority of my lucid dreams have only been from 10-60 seconds long, so I'm still trying to work on it.

Oddly, I seem to stay more or less lucid through the entire dreams, including that long 25-45-minute one I had (as far as I can tell, at least). I have yet to remember a lucid dream where I lost lucidity before it ended. On the other hand, I haven't had much luck with dream control, so I'm trying to practice that more.