Hong Kong Express Travel Card bus travel once activated

I was wondering if you could get the Express Travel Card with 2 Airport journeys to go from the airport to Central on Thursday 18th April and return on the Friday 26th April (8 days difference).
Can you also use the 3 days consecutive travel on the bus (after using on the MTR) to places such as Stanley? And would you be able to start using the 3 days 23rd April?
Many thanks for your help :)