The lease on static IP addresses continues until you either choose to delete them from your account, or until you cancel your CenturyLink internet service.
For qwestoffice.net customers only: Only one domain name can be assigned to a specific IP address. For example, ftp.mycompany.com and www.mycompany.com are considered one domain name. However, www.yourcompany.com and www.mycompany.com are considered two separate domain names and both could not be assigned to the same static IP address.
Note that moving or upgrading your service will usually require a change to your static IP address.