Night times

We are new to having chickens and have constructed a living area for them (3 in all) that is made up of a  ready made nest box with a small integrated run that is now in a much larger run approx 12ft x 12ft.  We have made the sides of the run from fence panels and wire netting approx 6ft high and dug into the ground a right angles to hopefully prevent foxes from digging under.  The nest box and run is in the middle of the run on concrete ( an area previously used for a greenhouse)

would the chickens be ok at night kept in the small run with freedom to get into there nest box or do we have to shut them into the nest box only?

There is a roof on the smaller run that is attached to the coop/nest box.  it is totally contained and I tend to leave them in there when I go to work and only let them in to their large run when i am home.