My LDs don't last as long as normal dreams, for me my dream times fluctuate a lot. My last LD lasted about 10mins or so, but really like the guy above me said it depends on your REM period.

And I dunno if it was me or i was just really lucky, it literally took me like 2 nights after i found out about this site to lucid dream (And yes when i found out about this site i tried to lucid dream)