not that easy ;)
training passing, i would do it when it fits on your schedule because when you play him there you will probadly have a problem at this game, and most likely in the others to when you train your C's in Passing ;)
I like the off season for such training, when you ain't planning with reaching the final - but sometimes you also could do it when you just have very easy wins or nearly impossible games in one week.
The next question would be, did you believe in Blocking and what skill you like to have in this skill at the end? Because if you plan to train it, i would do it early now because of the elastic effect so that the big guy skill are closer together as long as possible.