Premarket is in the Morning before trading starts at 9:30am. Aftermarket is after the market closes:
"Investors may trade in the Pre-Market (4:00-9:30 a.m. ET) and the After Hours Market (4:00-8:00 p.m. ET). Participation from Market Makers and ECNs is strictly voluntary and as a result, these sessions may offer less liquidity and inferior prices. Stock prices may also move more quickly in this environment. Investors who anticipate trading during these times are strongly advised to use limit orders."
