It's unclear how long the ban will last, but to me it doesn't really matter. Von Trier shouldn't be banned to begin with. First of all it's clear from his statements that he's joking. He even repeatedly interrupts himself to say that he's joking. Second, there's that whole "freedom of speech" thing, and for a Board that supposedly defends "freedom of expression", banning anyone for a few provactive comments is flat out hypocrisy. Third: Lighten up, folks. Seriously.
Von Trier has a history of making inflammatory remarks at Cannes, and they never led to anything like this before. The one mistake he made was in that half assed non-apology he gave. Y'know the one politicians use when they stick their foot in their mouth? The "If I've offended anyone" non-apology. He should've just not said anything at all or been a bit more sincere.
Regardless, this is all one big mole hill that has been bumped up to Everest status for no reason. Here's hoping all this junk doesn't effect Melancholia's chances of winning any awards. If you want to see the full context of what Von Trier said to light this fire, check out Slashfilm's recent coverage of all the Von Trier hullabaloo here.