Cooked a 1.5kg chicken next and cooked it to the time on the packet, 1hr 40m. Placed it breast side down for 30 minutes at 210 but turned it down to 190 as browning too much, and this with the ring on.
Turned it over and cooked for another 40 mins and it looked fine. Should have left it at that, but cooked it for another 30mins (as per packet) but turned out dry.
It seems that 1 hour is about right for this size, and that matches the recipe on here. But at least it was cooked beautifully all through.
It does seem a case of watch the temp., and turn it down if things look a bit too hot, but dont compensate too much , as I did.
Excellent first experience with a large HO, so glad I got it.