Just depends on the chick. I have 3 week olds that have more feathers then my one of my 5 week old. And if you put them outside for a few hours in warm weather they will feather faster. Usually by 5-6 weeks they start to look more normal, it seems like 3-4 weeks are the ugly stage in most chicks. All my BR, and my Red Sex Link was fully feathered by 6 weeks.
I have four 3 week olds, four 5 week olds, and I have been putting them outside all day long for the last few days, its been about 70, but all of mine do have fully feathered wings, and almost completely feathered backs, the 5 week olds almost have their head feathers in too, except for the one, it has like no feathers, probably going to be a Roo with my luck. I put them out in the coop with food and water, and if they want to come out, then they do. Today the wind picked up, and I went out to get them, but they were all sound asleep in the coop, so I just left them since they were out of the wind, and it was still 71. So as long as its warm, and they aren't huddling together to stay warm, the will be fine outside for a few hours.
Just so you know, when you do bring them back in the house, they all will crash, and sleep like babies for hours. At least mine do after running around all day long. The first time I brought them all back in I panic, thinking they ate something they shouldn't have, because they slept for hours, and even if I walked over, no one even looked up at me. They were tired out babies.