Try it with your own email

1. This is what your email would show

It ticks for a minute, like it does in an inbox, and shows the right time every time the email is opened. Open it again

2. Click through to the offer

This is the link your email would contain. Open it on another device too, and you'll see the same deadline there.

On your phone: point its camera at this code to open the same offer there. The clock won't start again.