During which lap did Lewis Hamilton take a pit stop during the 2011 Australian Grand Prix?
SELECT T1.lap FROM pitStops AS T1 INNER JOIN drivers AS T2 on T1.driverId = T2.driverId INNER JOIN races AS T3 on T1.raceId = T3.raceId WHERE T2.forename = 'Lewis' AND T2.surname = 'Hamilton' AND T3.year = 2011 AND T3.name = 'Australian Grand Prix'