180 days ahead of the actual amount of days you've played is the cap for pre-paying for days. No way around it. You can set up an auto-renewal for up to 180 days at a time and/or you can use the Game Time Cards to add 60 days at a time, but if you have more than 120 days left on the account (because 120+ days plus 60 days is more than 180), it won't let you use the card. I know this pattern all too well, since I always use Game Time Cards (can just buy em digitally now on Amazon.com) to bump my days to get the vet minions/mounts earlier. I'm sitting at 133 days and no way to get my darling little Nanamo for another two weeks because I have too many days left for another Game Time Card at the moment.