72-Hour Visa-Free Transit requires tickets from same airlines?

Hi, I'm planning to fly from Milan to Shanghai, then stop over for 72 hours and then fly to Amsterdam. So I believe I can apply for 72-Hour Free Transit. I have several questions:
- Does it matter the reason of the transit (tourist or business)?
- Do I need to book the flights from the same airline company?
- Do I need to inform the airline that I want to apply for the 72-Hour Free Transit prior booking the flight to Shanghai?
- How are the 72 hours counted in the Shanghai airports? From 00:00 following day to scheduled departure?