European - Asian and Middle Eastern Market Activity Sector starts at 07:00 am. If you look at the figure, you'll see that for Summer (April - October) this is the time when European stock exchanges enter the market. Trading still continues in Asia and overlaps with European Session.
During Winter, European Session starts an hour later but the Activity Sector remains the same.
07:00 am is the last trading hour of Hong Kong and either the beginning of the trading day (Dubai) or the first trading hour (Riyadh) on the Middle Eastern markets with a lot of action happening in both regions.