30 years equals about 11,000 days. One might assume that eliminating a few of those days would have little impact on investment performance during that time. Yet, if the ten best days of the S&P 500 Index for the period 1983- 2013 are excluded, the average annual return drops from 8.40% to 5.80%. If the twenty best days are excluded, the average annual return drops to 4.09%.
For example, the greatest loss for investors according to Dalbar data over the past 30 years came in October 2008. This was a volatile month; the S&P 500 started above 1,100 but at times closed in the 800s, representing a decline of 27% within a single month. Only the S&P 500 then rebounded somewhat and finished the month 14% off the lows. Clearly, October 2008 was a roller coaster of a month and relatively unusual in market history - we saw greater swings in October 2008 than are often seen over a whole year.
Limited trading hours help to reduce volatility in stock prices but also limits the liquidity of stocks. When trading hours are shorter more news reports and earnings reports are published while the markets are closed. As a result, investors have more time to process new information and general make fewer knee-jerk reactions. Read more about how trading hours vary around the world.