Although Forex is active 24/7, not every hour is suitable for scalping.
No scalper wants to sit in front of the monitor for numerous hours bored and disappointed with the “sleeping” price as it literally moves nowhere.
Scalpers hunt for volatile, liquid market. There are 4 major market sessions: London, New York, Sydney and Tokyo session. To trade effectively scalper needs to learn behavior of a chosen currency pair and define most active sessions, even particular hours for this pair to be able to catch good price moves.