What is the test for determining whether a word "shall" is to be construed as mandatory?

The People concede that it is ordinarily true that the word "shall" is to be construed as mandatory. When language in a statute is susceptible to different interpretations, the construction more favorable to a defendant should be adopted; "a criminal defendant is entitled the benefit of every reasonable doubt, in questions of statutory interpretation as well as of fact. [Citations.]" (People v. Lampasona (1977) 71 Cal.App.3d 884, 887, 139 Cal.Rptr. 682.) We therefore construe that word "shall" as establishing a mandatory time limit.