Free Range - new hens

Hi there,
I am new to the forum.  I live in Devon and have been keeping a few chickens just for eggs and their entertainment value.  Have just bought a few more as the cockerel was being a bit tough on 3!!!!.  My question is how long will I need to keep the new ones in until I can let them out with the others to free range all day.  They all live in a barn with a coop and perches at night.  The new ones are quite feisy at the moment and I dont want them to abscond before they find out that I run quite a nice hotel.  Any help much appreciated.
Ellie