Stay in SHA 72h transit visa (German citizen)

Hello,

if I take the 72 hour free transit on arrival in Shanghai and staying at a friends place it is mandatory for me to register at a police station as I understood ?

Furthermore the 72 hours are strictly defined after getting your "stamp" ? What if I arrive, check-in at the airport and due to various reasons the time exceeds to lets say 74 hours ? Could that be an issue ?

Thank you in advance.