Turns out if you don't log in you can vote again.

With that in mind.....

Just checked I can vote again on my Nintendo accounts at 7pm tomorrow.

So technically speaking one could vote for 28 different Heroes if you had to FE accounts (or used several computers without logging in, maybe more if you do this on every tech you have available to you)

Or donate all the votes to your favorite. It's your decision, and I can't force you to vote on what I want.