In my more recent LDs, I don't need any help, nor have any control over, waking up (grrr). But in the ones I used to get as a kid, which kinda freaked me out, I used to hide behind things, close my eyes, and when I'd release them I hoped I'd be awake.

Rarely worked though. If only my LDs nowadays were so unwilling to end.

On the subject of how long I'd like a LD to be without waking up; I'd say... a week? On the premise that I'd be able to get in again. But, according to LaBerge, dreams are entirely real time, so I guess there's an upper limit on the length of a single dream extending to an hour and a half or something, or perhaps even less.