New chickens

Hi we have just got our first chickens for eggs. They are around 4 months old and got them in the weekend. We currently have them in a coop but want them to be free range in an chosen area. How long would we need to keep them in the coop - I'm thinking that they need to settle in and know where the food is coming from, otherwise if they were outside free ranging won't they just fly away? They have been in coops up until now. Your comments would be appreciated.