I think that's the important point. You are unlikely to be blocked out completely, so how early you arrive really is dependent on where you want to sit. If you want to be front and center, then arrive early, but arriving later is not a big problem since most seats are excellent in my opinion.
Seats in the front portion are labeled "soak zone." The availability of those seats close to show time may depend on the weather. That means you may want to arrive early if you want those seats on a very warm day, or you may want to arrive early to avoid having those seats be your only choice on a very busy cool day. Generally, I think that you will usually find seats in the rear corners even close to show time.