Here's what the USCIS Policy Manual says about the so called 90-day rule:
"Although referred to by DOS as a “rule” in its Foreign Affairs Manual (FAM),
the 90-day rule is not a regulation. It is DOS guidance to its officers, and as such, the 90-day rule is not binding on USCIS officers. However, USCIS officers must examine all of the factors in an applicant’s case. After such review, USCIS officers may find that an applicant made a willful misrepresentation, especially if the violation or inconsistent conduct occurred shortly after the consular interview or admission to the United States.
[9] Officers should carefully assess each situation and continue to evaluate cases for potential fraud indicators. When appropriate, officers should also refer cases to Fraud Detection and National Security, according to existing procedures."
USCIS Policy Manual
Basically, the so called 90 day rule is a non-binding arbitrary discretion, there's no requirement for an IO to go by it. The IO will review the totality of your case in making a determination as to if you entered the US with the preconceived intent of filing AOS or not. If you're able to demonstrate you did not engage in any form of willful or false misrepresentation when you applied for your NIV, when you were admitted into the US, evidence to back up plans of departing from the US, etc. you generally should be okay regardless of if you waited 90 days or not.