What is the statute of limitations for discovery of an injury?

Plaintiffs respond that, as alleged in the complaint, they did not become aware of the injury until it manifested itself in 2006, the same year they filed their administrative claim. They assert that the statute of limitations was tolled until discovery, citing U.S. v. Kubrick, 444 U.S. 111, 119-22 (1979), and Davis v. U.S., 642 F.2d 328, 331 (9th Cir. 1981) (limitations period is tolled until plaintiff becomes aware of the injury), cert. denied, 455 U.S. 919 (1982). Defendant offers no reply to this.