Once you get the PWT demo tournament out of the way, it remains unlocked thereafter, though you might have to leave the building and attend to the Plasma Frigate cutscene before they have everything set up again inside. There are some restrictions on entering specific tournaments there (you can't do World Leaders without winning in each of the region-specific Leaders tournament first, for instance), and your team will be rescaled to 25 for Driftveil or 50 for any other tournament.
