Last night, i had 2 Lucid dreams in one night! My Dj
The most amazing thing was after i finished the first dream, i did a WBTB and jumped straight into the dream, already LUCID!
How is this possible?
This happens quite a lot to people who are familiar with lucid dreaming. It is sometime called “Chaining”. Basically, it means that you have not fully awaken, therefore when going back to sleep you continued with the condition of lucidity.
I’m having great results with chaining! I recomend you try it. 
When you wake up, don’t move at all! (This is easier when you wake up from a LD). Then just try to imagine some stuff, like you’re touching a wall. With some luck you’ll be in another LD in no time. 
Best method ever, period.
does chaining still work well if when you wake up, your REM period has ended?
Yes it will work, but it might not be as vivid.
How long does it take for your REM period to stop? Because once i’ve been awake for 30 minutes im thinking to myself “im completely awake now… its not going to work”
The REM period typically occupies 25% of total sleep, about 90-120 minutes of a night’s sleep. It occurs within 90 minutes after falling asleep and is divided into 5 stages.
hope that helps
source: wikipedia