I agree, there seems to be something wrong with Nabble's day counter.
I set up a forum on 21 October 2014 (that's 114 days ago) and today it tells me there's 66 days to go before ads appear. That's a trial period of 180 days, but, like you, I'm sure it said I had 365 days when I registered my forum and there's been no indication of a change of T&C posted on the
Nabble's Latest Features page.
You can find out exactly when you created your forum by clicking on your username and selecting "Account Settings" from the menu. That takes you to your Profile screen which reveals the date when you registered.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.