Lamb will take approx 30 minutes per kilo, plus 15 minutes. Alternatively a temperature probe is very handy. Insert into the thickest part of the meat half way in. It should read 50-55ËšC. Upon resting the temperature will rise to 60ËšC. Perfect pink roast lamb! If you like it a little more done, allow 1 hour and 25 minutes, or a reading of 65ËšC. Always rest before carving.