For HK Airport Express Card- do the 3 consecutive days of travel start on the day of arrival?

You must refer to Airport Express Travel Pass, right? Apart from one/two rides on Airport Express trains, you are eligible to the 3 consecutive days of free ride on MTR, Light Rail, MTR Bus (Northwest New Territory) (except additional ride on Airport Express, East Rail Line First Class, travel to/ from Lok Ma Chau or Lo Wu Station).

The 3 consecutive days starts from the recorded entry time of the first MTR ride, and lasts for 72 hours plus any additional hours up to the end of train service on the last day. :)