Players typically want to make Seasonal characters, as that is where the season journey and attached collection items can be obtained. Playing on the eternal realm will NOT grant the seasonal cosmetics.
The global release of the expansion is on the hour
If you are planning on making a seasonal character, you might want to try logging in early to get to the character select screen, but it is unclear at this time if a client restart is needed to see the Seasonal creation.
Seasonal is clearly listed as 4:30pm according to Blizzard's official site
