I have had this problem every time I recall having a LD. It seems like every time I was about to get somewhere or do something important, it was time to wake up. Granted, I’ve only had one LD where I knew what lucidity was and what the potential for experimentation is, but even still. I like Basilus West’s idea of repetitive focus, seems like the type of thing that would work for me.
There was the beginning of an off-topic discussion about LD’s and REM sleep. It was splitted and you can find its continuation here.