Redeem your code and restart your game
Go into multiplayer and click on choose playlist, it should show your remaining time
Restart your game, connect to online but sit in the screen that shows mp, zm and blackout
Have your friend search for any game
Once your friend is in a full game (the game being full is important)
Open your xbox menu and join your friend from it (dont use the social menu on bo4)
It will load for a bit then pop up and tell you the lobby is not joinable
As soon as it does, press A on the popup, click multiplayer and hit find a match
Complete the full game
Your double XP time will be frozen