One off payments vs subscriptions
At presscustomizr.com, we offer 12 months free updates when you purchase the default Unlimited Sites plan for a theme or a plugin. When it is a one-off payment, it means that the payment is done once to get 12 months update and the process is over : this is a manual yearly renewal and not a recurring subscription with automatic billing.
For a one-off payment, you can renew or not after 12 months. If you renew, your product will continue receiving updates for new features and bug fixes.
This is different than purchasing a Lifetime plan, which is a one-time payment allowing you to receive updates forever.
Renewing your plan
You can renew it at any time from your account, before or after expiration of your plan.