London - Beijing - Melbourne, then ten days later back the same way.

I think we should be fine for the 72 hour one (maybe 24 hour direct) but I was just wondering if it's 72 hours each time you travel into China, or whether that time is shared between inbound and outbound trips? So 36 hours in, 36 out, or whether it's a brand new 72 (or 24) each time you arrive? Thanks!