Can you use the return Airport Express ticket outside the 3 day unlimited travel period?

Hello,

We are coming to Hong Kong for a period of 8 days. It is not clear to me if the return trip to the airport will be valid after the 3 day unlimited travel period.

Can we buy the AE travel Pass with two trips (from and to the airport), use it to get from the airport to Kowloon, then use the card with unlimited travel for 3 days and then top up for the remaining 5 days before using the final trip to return to the airport? Or does the return airport trip expire at the end of the 3 day period?

Thank you!