What is the effect of a notice of failure to provide a reasonable time for completion in a contract?

According to defendants' own story they not only had, on March 21, 1960, collaborated in the continuance of plaintiff's efforts to meet the contingencies, but had frequently waived time rigidity in the culmination of the sale. Thus, even assuming that the trial court placed confidence in the verity of some parts of defendants' story, a notice giving a reasonable time for completion was necessary to reinstate such rigidity in the contract. As was said in Lifton v. Harshman, 80 Cal.App.2d 422, 433, 182 P.2d 222, 229,