Wondering if I am eligible for the 72 hour visa exemption, and how to maximize the hours?

I need a fresh pair of eyes to help me calculate the time so I may maximize my stay in Beijing. I am coming from Kuala Lumpur to Beijing. The flight arrives at 0105. I will depart Beijing to Singapore, with a layover in Manila. That flight leaves at 1255 on July 12. I want to maximize my full 72 hours, as I will visit a friend and pack in the sights. Would someone help me figure out how I can calculate the hours , so I can stay in Beijing as long as possible? What day could I leave KUL on, to be valid? Thanks in advance, very much!