If only you could spend days within a lucid... but I don't think time distorts in a dream. Especially not when you're lucid...
But, practicing lucid dreaming IN a lucid dream certainly sounds amusing. But, you'd need a task to do in the deeper LD as well.
I've found that I constantly need something to do or pay attention to while I'm lucid dreaming, otherwise I wake up.
So, as long as you have a tight plan, you should be good.