Will I buy the HK220 or HK300 for the airport travel pass?

I'm planning to take the Free shuttle bus K5 to Royal Plaza hotel after I arrive in HK. Can I use the Airport express travel pass HK220 in returning to the airport after 3 days. I don't understand about the single journey of the airport express pass, Is it used on the day I purchase it? or can I used it on the 3rd day in going back?