ahhhh, yet another clone thread.. (NOT HOW TO)

[PosativeHerb]

Hey all. got a prety simple question here...
took clones about 10 days ago... from strawberry cough and og kush.

NOW
around day 7 i had one clone showing roots... which was str cough.
figured ok this is a fast rooter cuz i had 2 diff moms...
BUT

thats the ONLY clone that has yet to show roots of that batch..its been 3 days since first showed roots and none of the others have shown any roots. i know some are rooted cuz i tried to pull one out (i know bad, but purely scientific) and felt a lot of HOLD, so assume its rooted, just not showing roots through the Rapid rooter. but others i have pullled in the name of science have no roots at all, look the same way as the day i took em, maybe a lil brown on tip where i cut 45 deg angle.
the same is true of OG KUSH, few have rooted, while others are taking their time.
i know ppl have waited up to 20 days for roots to show so im sure those w none will root soon, but my question...
why would a clone from the same mother root and the others under exact same conditions didnt root yet? i figure there would be some gaps in time, but havent heard of 3-6 day difference...
whas up with dat????