Let's see, that's a low of about 57F. At 6 weeks they are ready for 60F, so they barely need heat, if they do. They certainly won't in a week or two. (I can't think in Celsius!)
By all means, put them out there. And don't bother to run the heat during the day. If there is an attached run or yard, let them have access to that, too, during the day. They may not go out right away -- but that is often because of fear, not cold. They will know to go in for warmth if they need it.
I agree with Chickadee that heat lamps should always have a second means of securing them; hard to predict all possible failures of the hanging mechanism. After I hang them, I use a scrap of plastic covered metal clothesline wire, for example -- just what I have around. Too many coops burn down from heat lamps/lights -- and sometimes houses.