Hong kong stopover for 7 hrs: I wish to visit Madam Tussauds.

Actually, your time is tight. I'm afraid that you won't have enough time to tour around the museum because you'd better go back to the airport 2 hours in advance, and there will be a long queue waiting for the peak tram. Perhaps you can roam around Tsim Sha Tsui instead. Or take Airport Express to HK Station and then catch a taxi to the museum for fun.