Business multiple visa with no duration

Hi! I had before a residence and work permit, as I work for a year in china, it expired last November 2011, my company didn't renew the work permit, and just applied for a business visa, as I will go back to singapore as soon as I finished the trainings for my company's new restaurant in Guangzhou.

My question is that I have a mulitiple entry business visa with no duration stated on my visa. does it mean that I dont need to go out of china every month like the one with a duration stated on their F visa.

And another question, I will go to hongkong next month for a seminar, is there any requirements or supporting documents that I need to bring? I am a philippine passport holder, and I heard that it is very strict at the border to phiippine passport holder. What do I need to show Chinese immigration, when I enter back in mainland China.