The Elder Scrolls Online will release next friday, April 4th, but the early access kicks off today for the the digital Imperial and Standard Edition pre-purchases. Furthermore, the physical pre-orders will have access to the servers on April 1st and assure their three-day head start bonus, as Bethesda stated:
The three-day early access bonus that comes with pre-ordering the Physical or Digital Standard Edition of The Elder Scrolls Online from one of our participating retailer will begin on April 1, 2014.
Pre-orders are still available but the head start bonus is not longer accessible. The servers will launch early in the morning in the United States and late in the evening in Oceania. Check the five-day and three-day early access schedules for different zones.
Five-day early access bonus schedule:
North America (East): 7:00 AM EDT, Sunday March 30th
Central Europe: 1:00 PM CEST, Sunday March 30th
Sydney, Australia: 10:00 PM AEDT, Sunday March 30th
Three-day early access bonus schedule:
North America (East): 7:00 AM EDT, Tuesday April 1st
Central Europe: 1:00 PM CEST, Tuesday April 1st
Sydney, Australia: 10:00 PM AEDT, Tuesday April 1st
For more information about the early access schedules check the official news.