Agree with the cook much less than it says on the packet.
Especially for whole chickens. Cook for about 2/3 of the rec time, and most important of all, rest breast down for at least 15 mins.
It will carry on cooking and the juices will all go into the main bit you eat, rather than onto the plate.
I cook chickens about the size to feed 4 people for a bit less than an hour at about gm 6.
I also slash the thighs al la Jamie Oliver so they cook too.
Then stick upside down for about 15 mins
Foil on the breast is good too, take off for the last 20 mins.
And I know this is MN wank, but I buy organic from the butcher, which is about 6 quid for a 4 person bird, which does 2 adults and one child for 2 meals, plus makes brilliant stock (you can fanny about or just stick it in a pot with water and simmer for about an hour and a half)
That becomes soup or base for a sauce, so sort of 3 meals from one chicken.