It looks like your current highs are mid 80’s F and more important lows in the mid to upper 50’s Fahrenheit. (29 C to 13 C) I’d be a little nervous with only four chicks at those lows. If you have enough chicks they can generate quite a bit of body heat but four is not a lot.
If you have adult chickens in the coop you can have integration issues with chicks that young. I don’t think you have that worry but I’ll mention it for clarity.
If you can provide supplemental heat out there without causing a fire they can go out there straight from the incubator. That’s what I do, even with temperatures below freezing. As long as where they are is warm enough they are fine. They don’t care what it’s like outside their area. You don’t have to heat up the entire coop. Just give them a warm area to go to if they want to warm up, and give them an area to go to that is cooler if they want to cool off. They are really good at self-regulating that if given the option, even straight from the incubator. At three weeks yours should have no problems.
How fast they feather out are mainly influenced by how cool of temperatures they are exposed to, how high protein their diet is, and heredity. If these conditions are optimum most chicks are fully feathered by four weeks. Even if they are not great the vast majority are fully feathered by five weeks.
Chicks can generally handle cooler temperatures much better than people give them credit for. I’ve had chicks less than a week old handle temperatures in the upper 70’s by themselves, no other chicks or broody hens around. I’ve had chicks at five weeks handle overnight lows below freezing, but there were several and where they were had good wind protection.
If you don’t provide supplemental heat, I’d wait another week.