How often can the 72-hour free-visa transit be used?

I will be travelling to Guangzhou from Turkey arriving on December 28 and will have to clear customs and collect my luggage before checking in on my next flight which will be for Hanoi, Vietnam 6 hours later. I will come back to Guangzhou from Manila, Philippines on January 23 and have a transit time of approx. 24 hours where I will also have to clear customs and collect my luggage to check in for my next flight which is to Turkey.
My question is; How many times can I use the 72 hour visa free entry? If this can only be done once, do I need to apply for a one-entry visa or is it better to just apply for a double-entry visa?