Well I'm in a coco so it's a bit different but I only flush when I see it's all cloudy, but that's just me. Depends how you like your final product to be. I aim for 5-10% amber.
For me, once they're mostly cloudy I reduce to nearly no feed for a few days, plain water for another few days, then flush with Flawless Finish for a week and if I can, another couple of days on plain water at the end.
If they look like they've gone too far at any point during that time, i just pull em as I'd still take a slightly shorter flush over too many ambers. As you're in soil you shouldn't have any problems, in coco sometimes this is a bit too long for that plant to handle.
Depends on the strain though and what I'm looking for in it. Personally I would push a sativa a little longer to get a few more ambers as it balances the high a bit for me and gets rid of the raciness which I'm not such a fan of, indica I'm less concerned with and would probably take it when it's all milky with a few ambers showing.
I know there's a LOT of debate over flushing but as far as I'm concerned, the difference is night and day in coco/hydro but from what I can tell, it's somewhat less important in soil and not needed in full organics. Probably why there's so much debate over the issue. Best weed I ever smoked was organic and not flushed, worst weed I ever smoked was in coco and not flushed (my very first indoor grow) The longer I flush, the smoother my smoke.
To further complicate it, depends on your drying method. I've chopped too early before and let it slowly dry for two weeks (too long - they got a bit mouldy!), the trichomes continued to change during the dry. It was very clearly changing during the process. If you're drying for more like 7 days, you're probably not going to see much change though.
I'm not sure how much that helps, but that's my 2p.
it's only 110 Watt LED in 3 weeks she looks than bigger i think 
