stut

You can activate it any time on the day you want to use it, then it acts as a day ticket. Just make sure you've got enough charge on your phone! As the name suggests, it's valid all day in the whole region (Arriva only) should you need to use it again.

For future reference, the one-way ticket you buy on the bus is usually cheaper (though not always - my old commute to Luton changed the fares so the day ticket was the cheapest option, though not with my airport pass) and Arriva now accept contactless on all buses.

The app is quite good for bus tracking, too, so if the bus is late, you can see where it is.

corporate-wage-slave

I would probably have bought the £8 ticket in the OPs shoes. I'd imagine the cash fare would be around £4 or £5 but I'd be happy to pay a bit more for the convenience of a ticket which can be pinged when needed. If the OP's flight is delayed 24 hours it is still usable the next day or on a future day after being released from self isolation. Moreover with the day2 testing package presumably waiting for him, he may find the day ticket useful for getting the kit on its merry way. The OP now has the option to take the train to Maidstone and bus 12 from there, instead of Headcorn.

I'm not familiar with that m-ticket specifically, but there are two ways they work: either there is some sort of activation button on the ticket / app or you put it under the scanner by the driver and this activates the ticket.

DaveS

If I had been home, I would have been happy to give you a lift! I cannot improve on the advice given by others however. If you wanted to take a taxi from Ashford, Arrow Taxis is well established and has the easy to remember phone number 666666. Normally there would be plenty waiting at the station. I am not sure about now.