Sleeping patterns question

So however brief this question may be, it's something that could help plan for a good LD, or not. I was wondering whether in anyway shape or form a sleeping pattern maintains a certain pattern throughout your wakefulness. So we have REM sleep and NREM etc. which occurs at certain points of sleep (roughly), but does this carry on whilst your awake? Does your body track when these periods would averagely be, or is it always from the beginning of sleep. So if I planned to sleep for a certain period after waking up I'd be more likely to potentially have LDs or just a certain period of sleep.

Why in a WBTB do you have to wait a short while whilst when you first sleep you don't have proper REM sleep for hours? (and in-turn why would you have to wait a while to attempt WILD'ing with no prior sleep (not a main question)).