Sexing

I germinated and planted about 80 seeds and its been about 10 days now and i have 51 good sprouted seedlings growing under 2 cfl lights, and another room with 1 250W MH. Im wondering what is the best way to determine the sex of my plants? im trying to get 100 females by the end of May, as im planning to grow outdoor

Anyone!!!!!

They have to mature physically generally takes 4 to 8 weeks for that to happen.
You have way too many plants for the light you describe,somethings gonna have to give.

Should i put half under my MH ? and should i do the flowering to re-veg to determine the sex or?

What size pots are they in?

large paper cups for right now, im planning on buying bigger pots soon

I'd go get some 4' floro shoplights,yer gonna need quite a few.
That or a larger hid a 400 prolly won't be enough just to cover the square footage given yer plant count.
This is 2 4' twin bulb t8 floro shoplights and you see how many plants in 6" pots that will fit.

should i just get a few females, and clone a whole buch when i want to put them outside? how should i sex a few plants tho, by changing the light 12/12 then back to 24h? i only have 3 months until growing season starts

They really aint gonna show until they're physically mature.
I would def go the cut route if I was you.
Let'em veg until ya got about 10 nodes then try cutting back the light to 12 12,they should show relatively quickly by then.

Thanks that saved me a lot of hassle man, im new to this website never thought it would be any help

Time will tell all things,good luck and stay safe.