Technically it's not lengthening, it's using the fact that you were already conscious as you were waking up. You realize you're waking up, remain still, and then you can use DEILD to be absorbed into the dreamworld again, so it's kinda another LD in itself. I use it as safety-net for if my dreams become unstable. But yeah, I wouldn't push it, simply because I would probably begin forgetting stuff, or risk losing lucidity.

Up to you though. Doesn't hurt to give it a try. =o