The temperature in chicken raises by a rough constant in our experience. We usually are roasting chicken at 425 - 450 degrees F. If your chicken is not at the target temp you can roughly calculate how much more time you need. For a 4 pound chicken (~2kg chicken) the cooking time will vary depending on how cold the chicken is when cooking begins. If you took the chicken out of the fridge right before starting this recipe it is probably 35F-40F. On average the temperature will increase by 2.2 degrees F every minute when cooking at this 450F. If the chicken was 35 degrees F at the start and the final temp we want is 165 degrees F in the breast meat, then this is an increase of 135 degrees F. The total cooking time will be approximately (165 – 35) / 2.2 = ~60 minutes. If the chicken was taken out of the refrigerator a few hours before, it likely warmed up to room temperature ~65 degrees F, so the cooking time will reduce by ~15 minutes.