LAX to Philippines

Hi I'm planning a trip traveling from Los Angeles to the Philippines and I have a 19 hour layover in shanghai and on the return trip back from the Philippines to Los Angeles it's a 10 hr layover in shanghai I'm not sure what I'm suppose to do about the visa because I'm reading theres 72 hour free transit. Does that have to be applied way ahead of time and am I allowed to use it twice since there's a layover on the return trip