You can flower any time after about four weeks, so yes, you can flower now. Your plant looks nice and healthy, she’s ready.
@dave68 flip when they are 2x smaller then how big you. Want them they will double in size when you go 12/12
You can start the flower cycle any time past seeing pre-flowers, all strains differ, waiting too long will make the plant oversize and unwilling to finish all at once with new blooms shooting from old buds .
I put them in to flower today. I am hoping that deficiency will not hurt t ok much.
She is good flower anytime it’s nothing I would worry about at this time just make sure you ph your water and nutrients 
If anything she looks like she’s ready to flower
Al good advice i will repeat what @raustin mentioned that in most cases you can flower anytime after 4 weeks
The earlier you flower the lower the yield fyi
But as mentioned by @BigDaddyCain watch your two week streach cause they can double in size i personally do exactly what he mentioned and flower when 1/2 of my total available hieght
Remember to subtract the lights and distance needed from lights from actual grow space hieght
Getting worse. Really showing now. Looks like potassium deficiency. I have been using the bloom fertilizer.
That looks like a nuit burn not a def and burn and potassium look the same for the most part
Also I don’t see any flowers yet so you might have switched nuits a little early
Do you think I should try to flush them out?
No I do t think so what are you growing in what’s the ppm going in and what’s the ph going in as well as what the ph and ppm of the run off when you water need info light watts how far from plant need info if you could fill out the support ticket and we will get much more info to get you back to green and healthy. But with the pic I would say water plan water next two feeds then half str nuits on 3rd watering then scedule is when they are dry it goes water then nuits then water so alternate water and nuits helps stop the salt build ups and if ur ph is two high or to low it can cause lockouts of other nuits like potassium calcium magnesium.