For most games, it's cheapest to buy them right before kickoff. But for ND, demand is always high, so you might as well buy what you can early on to avoid getting shut out. For PSU, I'd start looking a few weeks into the season. If we get off to a strong start, demand for that game will be high and again, you may want to secure tickets early. But if we struggle early, you may want to wait until nearer to game time to get a good deal.
to play football, not to play trumpet