As an extra reward for maintaining a franchise for 5 consecutive seasons, you'll earn a $10 credit for a future season of Hardball Dynasty. After the 5th straight season controlling the same franchise in the same world, the credit will be distributed shortly after the final game of the big league World Series in the world.
So, if you joined a world in season 3 and stay with that franchise, you'll earn the credit after season 7, 12, 17, etc. The incentive is only credited after a season in which it was your fifth (or tenth or 15th or any multiple of five) season with the same franchise. And this will only occur for seasons concluding after the incentive program was introduced.