bamagirl,
I'm in central MS, and let my chicks out for their first excursion during the day at 3 days old, on September 8th for about an hour. I continued that until they were about 1 1/2 weeks old. I started putting them outside at around 10:30 am and bringing them back in around 6pm. This was about September 16th-19th. They were doing so well that I wanted to get them outside for good. So on the 20th, at 2 weeks and 1 day old, I connected their red heat lamp up into the portable coup and turned it on around 6pm. I went out to check on them around every hour until about midnight. They started out huddled up directly under the light, and I was worried they might be getting too cold and was prepared to bring them back in. But by midnight they had started spreading out. I checked on them again at about 4am and they were still spread out. At 6:00 am (dawn, all but 2 had flew up onto the roosts) This was also the coolest the outdoor temps had been. Around 75F. Every night since then they they spread out around the light and appear to be all comfy. They will be 3 weeks old the 26th this week.
I noticed from your brooder pic that you appear to have a larger light, mine is only 75 watts. So, even though your chicks are a couple of weeks behind mine, you probably have some options to work with because of our locale. You could set everything up outside, check on them like I did, and plan to bring them in only if they appear to be getting too cold. I did that, but things worked out fine.