Veg crop not sexing

Semi-noob, here.
I'm on week 8 of 16/8 in my little hydro setup, I've got a 300w LED panel and a 2x4 airscrubbed space. The plants are healthy with no spots/discoloration and are at a bushy 2.5 feet with thick stalks. They started out with some unhealthy looking roots that they shed in week 4 after their second flush, now they've all got nice white roots. I trimmed the tops off on week 5, and they're responding well to it except for the fact that they aren't showing any pre-flowers at all

I'm trying to get some clones going here and it's killing me, is there something that I'm overlooking?
I'm already off of my initial schedule to put them on 12/12 by two weeks, I've come to live with the delay but I'd like to get this show on the road already. Please advise.
 
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