The coop itself is small, but it is enclosed by a 6x12 dog kennel as a run, for 6 chickens. So that's 12 sq per chook. Then they have a 'chicken yard' which is prolly 18 x 36 or so. Assuming my math is right. ;)
Some feed companies recommend switching @ 12 weeks! At 12 weeks mine were only beginning to 'cluck' -- only when alarmed. So I think you are good depending on their maturity. You are feeding 'grower' or starter?