Question 72 h

In one of the comments is written, that the 72h transit starts from 00:00 / midnight

I arrive on monday 11th at 17:30 in in Beijing, coming from hkg. So clock starts ticking from Midnight monday to Tuesday, right?
We leave on friday Morning 2:30am to kuala Lumpur, that would be 74:30 but check in and go through passport control on Thursday at 11:30 pm. That would be 71and a half hours. Does flight leaving count or does it count when u r checked in and through the passport Control?