Registration (with personal data) in public store – using price scanner – 7 seconds without any action should interrupt?

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I'm creating a registration process to a loyalty programme that will be taken in public space (store)- Kiosk alike. Users will enter their personal data like: phone number, name, e-mail - so if someone decides to leave in the middle of process the data should be vanished (for security reasons) and the welcome screen will be presented> I tried to show the screen in the middle of the process with the time countdown: 7 seconds.

What do you think, how long should it take to automatically interrupt when no interaction from the user. Additionally, I added a kind of "panic button" that can be user If user want to interrupt on demand.

Users are very diverse: from 14 to 80 ye old... so it shouldn't make too much stress and on the other hand, I can't leave too much time so that anybody could see previous users data...

My main concern is, that when a user will look for their e-mail r phone number in their smartphone (for example) 7 seconds will remain for sure and all will vanish... so how much time should I give users to acomplish this step???