If you begin proving value 60 days before a contract expires, you have already lost the leverage. Value realization is a continuous process that must begin before the initial sale closes.
The Baseline
During discovery, the seller must establish the "before" state: how long a process takes, how much it costs, or what the error rate is. Without this baseline, there is nothing to measure success against.
The Review Rhythm
Partners must conduct regular Quarterly Business Reviews (QBRs) with the executive sponsors. These meetings should not focus on technical updates; they must focus exclusively on tracking progress against the initial baseline. When renewal time arrives, the decision is a formality supported by a year of documented success.