AI Timelines is the discussion of how long until various major milestones in AI progress are achieved, whether it's the timeline until a human-level AI is developed, the timeline until certain benchmarks are defeated, the timeline until we can simulate a mouse-level intelligence, or something else.
This is to be distinguished from the closely related question of AI takeoff speeds, which is about the dynamics of AI progress after human-level AI is developed (e.g. will it be a single project or the whole economy that sees growth, how fast will that growth be, etc).