when I feed my plants I go with a schedule of feed, feed, water the plain water is so you don't get to much salt build up. What nutes are you feeding ?its hard to tell in the pic but it looks like it needs some food
When’s the last time you took them out from under the lights to get a real see at what they look like? They are looking a very light light green almost yellow which indicates problems. And the leaves raking down toward the soil is another indicator of problems. To answer the original post. You can tie them down whenever you think the stock can handle a bend. Yours look like they could take it. I’d bend the shit out of them haha