I trade 9-12 and 2-4 sometimes. Never the day before or after a holiday. And my only overnight holds are on Dec.31st to Jan. 2nd.
I daytrade stocks: basically 9:30 - 11:00 and 2:00 - 4:00. From 11:00 - 2:00, it's churn and burn time. Make a little, lose a little. The momentum just isn't there.
False breakouts on light volume. All you do is end up giving back a lot of what you earn in the morning. The only exception is on a drifting day to the downside (yesterday was a good example); sometimes you can enter or hold a short and let it slowly sink through the lunchtime.