Yes, you can discontinue the light at that age with those temperatures. They are feathered out enough. My circumstances were different, but I stopped the light during the day a couple of weeks before leaving it off at night amd mine were off the heat light totally at 4 weeks. My lows at night were in the 70's then.
If they are used to light 24/7, you can expect them to protest some when it gets dark. It's going to be new and strange to them. It won't hurt them to protest and they will get over it pretty quickly, but be prepared.
I totally agree with ridgerunner. Actually if you follow the instructions from most hatcheries, it's
90 - 95 week one
85 - 90 week two
80 - 85 week three
75 - 80 week four
70 - 75 week five
After which, they don't need a heat light unless it's extremely cold and/or wet.
There was a post a while back and we were talking about judging the lamp/light based on their behaviour. Try to dc it, and watch them. If they are peeping loudly and hudddled together, they probably need it back.If you give it to them and they settle right down, you'll know you were right in giving them their light back.
My girls were doing their best to get away from the light and they are 4 weeks old. I have just moved them to their permanent lodging, so hopefully they do not freak out at the darkness. There are lights on in the yard throughout the night, so they will not be in total darkness.
I put my 5 weekers out with the big girls and rooster ( in dog crate in the coop) about 2 weeks ago. The first night was the coldest - down to 48 and I woke up at 5 in a panic and went out to check on them and they were fine. Since then they have done great and are now up on the roosts with the big girls at night - no more dog crate. Your little ones should do fine! They are tougher than we think!