You should probably first force them to stay in the square box by placing eggs in there and enclosing the whole thing with chicken wire or something similar so they can't come out for 2-3 days. Needless to say you will need to make arrangements for their food and water. You can worry about the chicks around day 18. At that point you can move them to safer place.
so when would you say would be the best time to do this? At night? Will try to find some chicken wire not sure if I have any but I think I do have another type of wire.