Any Airport Express or designated Mtr Customer Service Centre?

Specially designed smart card offering passengers convenient pre-programmed AE journey(s) and 3 days of unlimited rides on MTR (except East Rail Line First Class, Lo Wu and Lok Ma Chau stations), Light Rail and MTR Bus (Northwest New Territories). Can you explain a little bit more about 3 days of unlimited rides on MTR? My question is, If I start to use express train to city at Oct 1st in 9pm, what o'clock is the finish of my express travel pass? Is it Oct 4 at 12pm? Or Oct 3 at 12pm? Thank you