From an index (S&P/Nasdaq/Dow) perspective, classic wisdom says the average day goes like this:
9:30 to 10:00 am - trading range
10:00 to Noon - higher volume part of the day - counter trends
Noon to 1:00 pm - lowvolume..naptime
1:00 pm to 4:00 pm - more of a trend, but lower volume
lately the last hour has got the better trend
Bonds close earlier and make a little hiccup in the afternoon.
Caveats:
1)The times are approximate.
2)Every day is unique. A good trend day, such as 3/25/04, does not look anything like the average day.
3)It is up to you to determine if this 'Classic Wisdom' has any truth to it.
So, staying away from any particular part depends on your own trading style. We all find our own niche and trade there.