Airport Express Single Journey in HK: validity

I will arrive in Hong Kong from Mainland China on Saturday April 12th.
If I buy an Airport Express Single Journey Octopus card on Saturday, I can use it for 3 consecutive days in HK: i.e. on Saturday, Sunday and Monday.
I leave from HK airport on Tuesday = the 4th day.
Is the single journey from HK to the airport on the airport express valid?