Btw, in case anyone else didn't think of this either, like me:

Someone pointed out on reddit using Fantasia requires a log in for using the item, then logging out, do the changes, and then logging in again to see the result. So plan some time for your transformation into your personal big cat queen, considering the queues are likely going to be long. It's also not entirely clear to me if you can change when you're not on your home world, so going to a less congested world or datacenter could cause an error when trying to fantasia. Do this at your own risk.

Of course you can save a step by using a Fantasia you already own, but the potion is going to be changed with Dawntrail, and it's unclear if already activated Fantasias will have this new 60 minute timer as well.