Earliest time to flower a plant

I was thinking about this issue before i planted them in the space, but thought i could do it, so as i put the light in, it was bigger than i thought. I do it anyway. there definately isnt enough head space for a 30" plant and a 400 watt hps. but i reckon it is do-able to grow just a small plant in there. so now its growing, and im asking anyone who wants to answear. What is the earliest time you can flower a plant?
The strain is thai/jamaican

once it has 4 nodes it's good to go. Dont' expect a great yeild though.

I've got a couple I started flowering 1 week from seed & they are probably 16" & 20" tall. They are not through growing yet but I don't think they'll get more than 3" taller.

just to let you know sativa dominant strains will more than double thier size when put into flower.Peace

if they more than twice as high, i should put them on 12/12 when they are about 6 or 7 inches then?? wot kind of yield can i expect if i tie them down to minimize their height??

transplant it into a 5 gal bucket ... cut about 5 inches off the top of bucket & use the LST method... it really works with great results ,, i flowered 3 weeks from seed ,..using the LST method the whole time in vegg ... ., topped at 3rd node . i wasnt exatly sure how tall my baby was due to being tied down in the sprial LST style...BUT that plant & 1 other plant , plantted at the same time ... 1 LST style topped a 3rd node & flowered in week 3 ,,, and 1 plant toped at 3rd node & DIDNOT use the LST on this one ... got 1/2 oz , the LST one i got 1.8 OZ's

veg 10 26watt 6500k cfl's
flwr 1 150 W hsp 4 monster 100 W 2700K cfl's ,, * side lighting