we all talked about this in another thread but there is no right answer.
Spring Training = players might not be fully ready. players have to balance competing in the WBC with things like trying to win an MLB roster spot, or gelling with new teammates.
After World Series = players are tired as f***, burnt out. added innings for pitchers might have increased injury risk at this time?
Middle of the year = you'd lose the All Star game every 4 years and the MLB schedule might need slight changes. May need to contract WBC to fit in shorter timeframe.
Maybe they should do it DURING the MLB playoffs? I think the world hockey championship used to do this, or does do this. Players can join their country teams if and when they get eliminated from league play.