What is the statute of limitations for naming an unknown defendant as a plaintiff in a defamation action?

Under section 474, "[a] plaintiff ignorant of the identity of a party responsible for damages may name that person in a fictitious capacity, a Doe defendant, and that time limit prescribed by the applicable statute of limitations is extended as to the unknown defendant. A plaintiff has three years under section 581a, subdivision (a) after the commencement of the action to discover the identity of the unknown defendant and effect service of the complaint. [Citation.] When the complaint is amended to substitute the true name of the defendant for the fictional name, the defendant is regarded as a party from the commencement of the suit." (Munoz v. Purdy (1979) 91 Cal.App.3d 942, 946, fn. omitted, 154 Cal.Rptr. 472.)