First time grow, almost ready? Need advice

Hey all,
This is my first grow, so please excuse the ig'nance! The time draws nigh for plucking & curing I believe.. I need some advice on how much longer I have please! I started with 5 seeds and 4 turned out to be girls, so my box has been a little cramped. I'm not complaining, it's great having quadruplets! Dad couldn't be happier .. However it definitely made for slightly unhealthier and lankier plants.. That being said, here is some info..

- I'm growing Hindu Kush under a 400w HPS (4 plants)
- Nirvana said with this strain, 7-9 weeks for flowering
- I'm in the middle of the 6th week
- I just watered them with nutes tonight (for the last time?)

I'm wondering if my girls are about ready? I definitely don't want to pull them early, so I was hoping I could get some advice on how much longer (give or take) I should wait..
It feels like the buds might grow a little more, especially since I'm only 6 weeks into the flowering cycle and they're supposed to go ~8 .. However almost all of the big leaves are yellow, and the only green ones anymore are around the buds.

Can I keep them on life-support? Should I stop with the nutes? I gave them a pretty good dose of FoxFarm Big Bloom tonight (4 tbsp in the gallon) and I'm thinking that might be the last time they get nutes. You can't really see in the pics (HPS lights make my cameras do funny things apparently!) but probably 20-30% of the white hairs have turned brown .. I know I'm supposed to be waiting until 80-90% of the hairs are brown but all the yellow leaves make me think these buds aren't getting all of the light they'll need.

Any advice is appreciated, don't be shy! Like I said this is my first grow and I've been impressed with their growth thus far. I waited too long to get the HPS so they're somewhat tall and stretched, especially towards the bottom. But when I started the flowering with this new light, they grow about 2.5x their previous size! I thought I flowered them too early, turns out 3 out of the 4 pretty much outgrew the light. Yiiikes. But again, I'm not complaining!

Any thoughts? Thanks for looking!

looks like they got a few weeks left. you could keep nutes going for another week if you want. Seems like all the pistils are white still. Also, dont judge it by the hairs. Get a jewelers loup 30X, and look up how to tell by the resin glands. They need to be cloudy, or turning amber in color. Not clear. Thats the real way to tell if they are done, the hair thing is more of an estimate.

Probly 2 more weeks to go bro. Buy a $12 scope @ radioshack or wherever....you worked this hard for this long, don't let $12 come between you and a proper harvest