In August 2000 the Singapore Stock Exchange introduced a pre-trading routine that allowed brokers to place orders into the Exchange’s computerized order matching system for a period of 30 minutes prior to market opening. A post-market trading routine was also introduced allowing for a final order matching and trade execution to occur five minutes after market close. This study investigates the impact of these changes on volatility and the price discovery process. The pre-trading session significantly reduced opening stock market volatility while the post-trading session increased volatility prior to close. A GARCH (1,1) model remains the most appropriate model for capturing the characteristics of the intra-day stock price movements in both before and after periods.