So basically anytime you wake up you go back to bed. There is no really time limit but its better to do it early then waste you dream.

1. Lay on your bed, or just stand I guess. Then try to imagine an image in your head. Then you should see a world start before you eyes.

2. You only have to wait 20 seconds or less. Because for this to be most effective... You already have to be in a dream. (Preferably a false awakening once)

3. Once the image is better move around.

I did it once with my eyes open! (in dream)

Do it before you go to bed and especially when you wake up. To make sure your not in a false awakening.
You will rarely know if you had a false awakening or not. So do it every time you wake up.

I keep doing this one accident in my false awakenings (trying to become lucid) and it works many many times.
You can get multiple dreams in just one.