Much less time than you might think. When a public agency operates the bus — a city transit line or a regional transit district — a claim generally requires filing a formal government claim within a short window, often about six months in California, rather than the two years that applies to an ordinary injury case.
This is a trap that catches people who assume they have the usual amount of time. Missing the government-claim deadline can bar even a strong case entirely, which is why identifying whether the bus was public or private, and acting quickly, is so important.
There can also be a question of which public entity is responsible, since a bus may be run by a city, a county, or a regional transit district. Identifying the correct one and meeting its specific deadline are the first urgent steps, so getting advice promptly protects the claim.