HKIA - Macau - HK island - Airport

I will be visiting HK and Macau this week, but I will go straight from the airport to Macau via Ferry. I will return to HK at the HK-Macau Ferry terminal near Central Station in HK Island. So my question is can I buy the HK$220 single journey to the airport tkt and use the 3 days before using the single journey on my way back to the airport? Also should I buy it at the Airport before going to Macau or until I get back at Central Station?