What is the limitation period on a plaintiff's legal malpractice claim?

In Budd v. Nixen (1971) 6 Cal.3d 195, the court held that the limitations period on the plaintiff's legal malpractice claim did not begin until plaintiff had suffered "appreciable harm." (Id. at p. 200.) "The mere breach of . . . duty," said the court, "causing only nominal damages, speculative harm, or the threat of future harm 3/4 not yet realized" normally "does not suffice to create a cause of action." (Ibid.)