What is the test for "premeditation" in the context of the murder of Roberta?

Under Arizona law at the time of Roberta's murder, "premeditation" required that the defendant act "with either the intention or the knowledge that he will kill another human being, when such intention or knowledge precedes the killing by a length of time to permit reflection." Ariz.Rev.Stat. 13-1101(1) (West 1978). An act was not done with premeditation if it was "the instant effect of a sudden quarrel or heat of passion." Id. Premeditation could, however, be "as instantaneous as successive thoughts of the mind." State v. Kreps, 146 Ariz. 446, 706 P.2d 1213, 1216 (1985).