Brought mine over right towards the end of systems ground school, which tends to be about the 5-6 week mark. Works out pretty well, as after that you generally have about a week or so of just some emergency training, FLI workshops, CRM, whatever, before you actually start simulator training-its pretty laid back and you'll have plenty of time to do other things. Since you'll be in the simulator periodically during systems ground school, you should already have your flows and procedures down pretty well, so there's not TOO much to study during that time frame. Also, after Systems everyone's ready to go blow off some steam, so it usually ends up being a pretty fun weekend.
Some of the boys waited till LFUS to bring their wives over. The problem with that is your roster changes quite frequently, so often the guys would be off, bring the wife over, and then end up having to fly. Besides, you'll get a chance to do a frieghter trip back to the states and go home for a week or so sometime during LFUS and get to see her then.
Cheers