No.. if you want to pay 90 days upfront you can so you get items asap. If you decide to just play as normal and pay monthy you will get the items in due time. Either way you get the items jsut depends on when.
"Veteran Rewards: various bonuses depending on how long you subscribe. Includes different subscription models. If you do 30, 60 or 90 days there will be thank you gifts such as pointer minion (30 days) and different mounts. Another is a character remake ticket. Black chocobo chick and black cascadier uniform (swimsuits) voucher for 60 days. Ahriman minion and Ahriman mount for 90 days. Will have 120, 180 day subscription models for more rewards. You pay upfront for the time and then you receive the rewards. For example by starting with a 90 day subscription, you receive the 30 day and 60 day rewards on top of 90 day rewards."
I hope you're right, but judging from the notes, it's not confirmed.