I have 3 chicks that will be 2 weeks old on Thurs. I am getting 51 day old chicks on Sat. The large group will go into the large brooder box in the barn. The 3 older chicks have been in the basement in a plastic tub brooder. They need to get into a larger area. I would like to have them all in the big box. Would it be better to put the 3 in there now then add the little ones on Sat? or should the little ones have the box first, then add the older ones at a later date? The big box is about 5'X6' and approx 30" tall. the older ones will have flying room, as they don't have that option now and are getting tired banging into the hardware cloth on the top.