While the decline is indeed steep, missing up to 30 seconds is still not that large of an effect, and of course this is a fairly rare situation. In this case, I suppose the 6 fouls are a pretty good clue.
It isn't a massive drop. It does drop (probably by 10% but that is just a guess) but its not worth worrying about. You are much better off using your next game to train a different player for 48 minutes rather than play this player again just to get him an extra 20 seconds.Hope that helps.