Latest date of entry for a double entry tourist visa.

I have a double entry one with 30 days each. If it says enter before 2nd June 2015 does that mean that I have up until the 2nd of June to make my first entry into China and I can then enter for 30 days, leave for 7 days to Hong Kong and then return for another 30 days? Or must my second entry begin before 2nd of June and then I can continue to spend another 30 days in PRC?

Thank you