Correct; the 200 bucks would go on whatever card you have now.
Visa doesn't know when your vacation actually occurs, they only know that you charged an amount that qualifies for the 6 months no interest loan.
I've always paid in full at the last possible date and had that much time to pay it off.
Keep in mind that any purchases you make at WDW while you're there don't count; you'll have to pay them off normally. Visa will call your vacation loan the "interest saving balance", and the app will actually double check with you if you pay it off early.