Maximum hours stay with an 144 hour visa free transit

I intend to arrived at PVG on 08.00 on 31 DIC 2018.
That means:
1) that my departing time must be before 23.59 on 6 JEN 2019?
2) my departing time time could be after the 23.59 on 6 JΑN 2019 ( p.e 05.00 7 JAN), but I must passed the passport control before the 23.59 and rest into the PVG transit area until the departure time?
And please another thing
3) the inbound and outbound flights could be in different tickets ?
Thanks for the answers.