I normally bring on a couple of subs at around 60 minutes, and nearly always attacking players. I go by the logic that these players will be fresher and more able to make an impact in the final third of the game. Sometimes it seems to make a difference, sometimes not, but I do think the possession bar seems to go more in my favour for a while after I've made the subs. I mostly make a third sub late in the game, for a very tired player or a carded player.I hardly ever change the defensive players though, way to risky.