General

Cash shop items expiration

I want to buy NX from a guy with great rates, but I'm buying a shop permit, and mine expires in a month,
This guy will not sell NX after a few days.
When is the time stamp created on a Cash Shop item?
Because I would like to buy a shop and then use it after a month without losing 30 of the 90 days by finishing the other shop permit I have.
Thanks