Does "enter before" only refer on the first entry or also on the second entry?

If I get a tourist visa (double entry) for china, I am allowed to enter twice for 30 days each stay. Do I have to enter the first time to china before the date that's fixed in "enter before" and can I enter for a second stay after that fixed date? Or do I have to enter for the second time before the date that's fixed in "enter before"?