Activision has a note on the site saying = Please note: If you pre-purchased a digital copy of Call of Duty: Black Ops 4, you are already registered for the Beta. Your status won’t be displayed on the redemption page.
PlayStation 4 = STARTS September 10th at 10am PT / 5pm GMT, and ENDS September 14th at 10am PT / 5pm GMT
Xbox One and PlayStation 4 = STARTS September 14th at 10am PT / 5pm GMT, and ENDS September 17th at 10am PT / 5pm GMT
PC Users: Call of Duty 4 Blackout Beta starts – September 15th, 2018, on PC.
Early Access starts August 10, 2018. Actual platform availability and launch date(s) of Multiplayer and Blackout Beta subject to change. See callofduty.com/beta for more details. Limited time only, while Beta codes last, at participating retailers.
Check out Activision’s Beta Q and A here.