I think that depends on a few things. How much protection does that tractor give them? Do they have an area they can get out of the weather day and night if they want to? Some tractors can be pretty open. I'm thinking about both wind and rain. I've had brooder raised chicks start roosting anywhere from 5 weeks old until 12 weeks old. Some people report having to wait much later before they start roosting. My point is how do they stay out of the weather during storms. Outside Shreveport like you are, cold is not your problem this time of year, but a rainstorm might be.
Heat can be a big enemy. Yours will need protection from the heat, so make sure they have a shady place to go during the day and that their sleeping area is well ventilated.
Have they been acclimated? I don't do real well going from a cold place to a hot one or hot to cold. I need to get used to it a bit. So do they. I think they feather out faster and are able to handle different temperatures better if they have a bit of an adjustment time. So what is the weather like (severe versus mild, stormy versus calm)?
Those are the things I'd consider. Now some of my experiences. I've had a broody hen take her chicks to the roosts at 2 weeks in the middle of the summer (lows at night in the lower 70's). All the chicks could not fit under her on the roosts. A couple even slept on the top of a 2x4 brace (narrow side) nailed to the wall so they could not even cuddle and keep each other warm. They were playing in the weather from the day she took them off the nest.
Again in the middle of the summer, I've seen chicks with a broody sleep out from under her, resting on her at night. If they get cold they can hop down and crawl under her to get warm, but a broody is a lot more casual than I am about keeping her chicks warm.
I keep my brooder in the coop. It is fairly large and I only heat one small area. The rest of the brooder cools off to ambient, whatever that is. Last fall, it was sometimes in the 40's or 50's at night. They did sleep in the warm area but would play all over that brooder when they were awake. I took them out of that brooder and put them in an unheated grow-out coop at 5 weeks age. It was well protected against drafts, but certainly not heated. There were 14 of them so they could huddle and help keep each other warm. When they were 5-1/2 weeks old, the overnight low was in the mid-20's. They were fine. I went down to check on them and they were just sleeping, not peeping or complaining at all.
Again in the middle of the summer, I've turned the daytime heat off at 2 weeks and the overnight heat off at 3 weeks. It depends on the temperatures and how they are acting.
I've had broodies wean their chicks as early as 3 weeks and some as late as 9 weeks. The earlier they wean them, usually the warmer it is, but that 9 week one was also in the middle of the summer.
In your area this time of year, I'd watch the storms, but I'd probably wait until sometime after 4 weeks but no later than 5. Even if they have not been acclimated at all, at 5 weeks they should be more than ready.
Good luck!!!