Very Slow Flowering?

Hey everyone I have three Grand daddy purp plants and 2 of them are almost done. I tried to squeeze 3 nice size plants under a 400 watt HPS but I've read a 400watt only covers about a 4'x4' space so I put 2 almost directly under the light and one is pretty far from the bulb. They are all about 5-6 weeks into flowering and 2 look like they will be done in like a week to 2 weeks. The one the furthest from the light looks like its in like its 3rd week of flowering but its been about 5-6. Its got White hairs all over it and looks like its trying to form buds. My plan was just to move it in place of one of the other plants when one of them finishes up. Do you think it will still fill out when I move it under the light even though its already like 5 weeks in? Let me know what u guys think. Thanks again

Yes it will still fill out, just take a few extra weeks. Next time maybe rotate the plants every 3-5 days so they all finish around the same time.

your density will suffer without proper intensity. speaking of which, the buds on top closest to the light mature first and get the densest. In a tent, i have and would harvest your primo nugs first once most(at least 80%) of the white hairs have turned brown and receded back into the bud. Cut those beauties back and let the lower canopy go another 2 or 3 weeks with more intensity and you will reach happiness. I harvested 1.5 pounds on a 600w this way.

Thanks guys I appreciate the help. I def feel better now knowing that I can still properly flower the plant once I move it directly under the light