LAY OVER

I am flying to Sydney from LAX for a one month holiday. On my flight to Sydney I will not be leaving the airport because my layover is only 3 hours. However, on my way back to LAX from Sydney I have a 8 hour layover and I am wanting to leave the airport. Would I be able to use the 72 hour Free Transit on my second trip back into China, or since it is technically my second time visit would I need a different one? Any help would be great!