I really dont care about that, i put my formation whend i have time to do it, it can be at the end of the day or only a few minutes before the match.

I make adjustment to my tactic, but i play only the formations i like to, depending on the players i have available.
I have seen that people that make to many changes in formation during the match, end up to have bad results.

As seanmeg said the engine only makes the simulation 3 minutes before the match.