At least a year. If he doesn't do well, they'll probably still stick with him for at least a season, because, bizarrely, they've been obsessed with him for quite awhile. If he does do well, he'll get enough offers to return to the premiership. It certainly won't be as easy as he probably expects it to be - he really has to learn the language, for a start, and it's not a club that will help him to 'prove' that he's capable of managing at a bigger club than Everton, so at best he'll be back to where he was a couple of years ago.