This solution doesn't require your active participation unlike the two methods already provided.
First, go to any desert area in the game. (Qattara Desert, Iment Nome, Isolated Desert, Black Desert) Wait there until you see a hallucination, it's usually accompanied by a sound queue. Wait in the area for a few minutes to ensure it's safe from attack, meaning there are no animals (lions, hyenas, jaguars) that will attack you, nor any convoy routes that pass through there. After that, just wait.
Additionally, if you want to leave your console alone, you can do some of these things:
- Go to your Xbox's Settings > Preferences > Idle Options and turn off 'Show me things when idle'. If you go idle, ACO will pause.
- Go to your Xbox's Settings > Power & Start Up > Power mode & startup and set your Turn off after option to 'Do not turn off automatically'.
- Plug your controller in to the console so it does not turn off.
There have been some reports of it taking people up to 11 hours to get this achievement, so you don't want to have to run around or even pay attention to your console while trying to get this.