How quick do you enter REM sleep during the middle of the night

Title says it all, and I know that during the middle of the night REM sessions are closer, but how close, and when I do a WBTB is it a problem if I awake during a REM session and/or after it. Because they say it is better to awake before one

I also had my first lucid dream and I noticed after my WBTB after I went to sleep I entered the dream SO QUICK like 5-10 minutes, will it be longer if i awake during or after a REM session???

It depends on how fatigued i am. Usually takes awhile for me.

When some people enter Sleep Paralysis their eyes start flickering around and their body's trying to enter it immediately... so my guess is right away. I'm sure some expert will tell you an exact time though! Although it probably varies on each individual person and your sleep cycle.