I am a US citizen on a student visa in HK. I have a multiple entry visa to China. It says that I must enter before July 4, 2010, and the duration of each stay is 30 days. Does this mean that I can enter China before July 4, 2010, 24:00, and then stay for a month after that, or do I need to be out of China by July 4, 2010, 24:00? Thanks so much for your help.