All our premium themes comes with initial 1 year of Subscription. This means that you can download the updates and get private support forum access till 1 year of purchase date. But after one year, you will need to renew your subscription in order to continue downloading updates and get private support forum access.
But this subscription has nothing to do with the usages of the theme to your site. You can use it in your site as long as you want it without renewing your subscription.
Another question: Once I purchase a theme, I obviously cannot use it more times. The theme I’ve purchased seems to work even before activating, thus I’d like to ask what happened if I use this theme on another WP-Instance without activating the 2nd instance.