A long time ago I used to be totally confused by the AM action and only traded after the first hour of trade, but then I realized that if you come into the day with a game plan and look at the previous day's trading as well as the overnight action, it gives you a much better chance of profitably trading the morning market. I make most of my bones now in the first 90 min of trade.
The afternoon trade to me is a lot of noise unless there is a strong trend or big volatility. So probably 8-9 times out of 10, it is noise.