i recently transplant all my plants from styrofoam cups to bigger pots except for my fastest growing plant which is in a double gulp cup from 7-11 it holds like 64oz i believe....how long can i keep it in there?...SINCE IT WAS THE LAST TO GERMINATE AND TWICE AS BIg as other i think its prolly male...good assumtion? and can i force flower it to sex it in there?

No assumption is a good assumption for plants, ive had a few that looked like they had beards and a belly, but later took the form of bud,could be just better genetics in that seed

You can keep it in there as long as the roots do not get bound.
Here is great post from rollitup: Check it out.

Pot Size

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Chiceh
Peace, Love & Weed

thanx thats what i suspected.....the double gulp is 1.9liters and i have to keep my plants around 21" fully flowered can i leave it in there for the duration? also when should i start on 12/12 to keep them that height?...

You could always top it. Cut the top 3 inches off to keep her small and bushy. And as a bonus, you can clone that top and make another plant. Cool eh?
But to answer your uestion, you can flower her anytime once she has a few branches up the stalk. Maybe 6 inches.

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Chiceh
Peace, Love & Weed

What medium is in the cup. If it's coco...then it will be fine. But 8 more weeks or more in soil just won't do. She will peter out and be too stressed half way through flower.

Drink!

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"The art of medicine consists of amusing the patient while Nature cures the disease." -Voltaire

what did you mean by coco father jack or anyone for that matter?

coco coir, coconut coir, coco chips et al.

A growing medium made from the husk of a coconut that is far superior to any peat based mix in water retention& ph stability.

Coco growing medium is a natural resource that isn't ruining the bogs that peat is mined from that took 1000's of years to create which are a habitat for lots of wildlife.

Drink!

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"The art of medicine consists of amusing the patient while Nature cures the disease." -Voltaire

I've seen pure bud clones a foot and a half long as thick as the average persons forearm
grown out of halves of 20 oz soda bottles. (I don't recommend this for Newbies, For newbies I would say use as big of a pot as you have room for)