Best case, all of that takes 6-9 months, but the reality is more like 12-18.
Having time to understand the "why" behind features in a deeply critical way is a LUXURY given this average 2-3 yr time frame. And all of this assumes an absence of reorgs, mission-critical integration work, etc., which further complicate understanding.
The reality is that customer needs are changing so rapidly that even CEOs and heads of sales fail to grasp the "why" most of the time, and merely focus on just doing whatever it takes to win the next big contract. "When one can see no future, all one can do is the next right thing."