Entry L Visa Requirement

I have a Visa granted to enter China. It's a double entry valid until 22July 2013. I intend to visit Beijing on 15th July, 2013. (1st entry). Then proceed to Macau on 21July2013 until 24th July2013 and back. However my Visa will expire on 22nd July 2013. Please advise if I have to re-apply for another Visa to re-enter when I am in Beijing and how many days will it takes and where should I apply?