Well, my lucids typically last a whopping ten seconds. Needless to say, I need a bit of work on the whole stabilizing thing.

I would assume that a well-stabilized lucid would last about as long as a regular dream. Possibly longer, since there are stabilization techniques and stuff, although I'm far from an expert on that sort of thing.

Plus once you do wake up from the lucid you can DEILD back in, which can make them quite long (even though it's really a string of dreams).