Calculation depending on scheduled departure or passing of immigration?

Hello altogether!

I am planning to fly to Shanghai and arrive there on the 20th of July.
1. So the 144 hours would start counting from the 21st at 00:00 and go until the 26th at 23:59. Is that right?

My flight to Japan however is on the 27th at 01:10. But of course I could still pass the immigration on the 26th before 23:59.
2. Would that be possible? Is the calculation of the 144 hours depending on the scheduled departure of the flight or the actual passing of the immigration?

Thank you very much!

If this is not possible, I will just change my flight going to Shanghai to the 21st. That should be no problem, right?