Hi, I've 6 months double entry visa from (2 August - 2 February 2017)

My friend told me that it's basically 4 months entry permit, I've to exit from China after every 60 days , but my agent told me that at first I've to exit from China after 60 days, later I can exit after 4 months, that makes up total 6 months, so it makes me confuse, I don't know whose statement is true about it, kindly help me out , ....