MasterMark wrote: does anyone know until what time i can change my formation on game day????

1 hour before the match

That is you can do it up until 1 hour before.

So for a league game, since yours start at 15:00, you could change your formation up to 14:00. After that, the changes won't go through, and if you hadn't set them at all until then you'll run with a bot lineup.