Did I overstay and when to exit China?

Hi.
I have a multiple entry business type with "Enter before Oct 24. 2015" and I entered China on Oct 22. Duration of stay is 90 days. Did I overstay or I am allowed to stay for 90 days starting from Oct 22?

I am asking this because I have heard that it is allowed to stay until the date stated, no matter of is it "Valid until" or "Enter before". Thank you