ICly speaking, that's correct! That blurb takes place on October 31, which also coincides with the day the Pokemon Centers will begin handing out the antidotes that will reverse the Fusion Effects en masse. (Which was mentioned in a previous infopost and didn't make it over to this one, sorry about that.)

So ICly, it will last until your character takes the antidote, but for OOC purposes we're understandably assuming that characters will be relatively expedient about getting themselves to a Pokemon Center to get that reversed. o/