Hot Week: 1/5 – 1/11

And if you participated on the same character every day this week,

Gonna have to make a note on my desktop to make sure I don't screw this one up.

It will probably still work if you do it on different characters in the same world. I doubt they've changed the programming. They just don't want to deal with people from allianced worlds complaining.
However, best not to risk it if you don't have to.