If outside the US , No. It is illegal to enter the US as a visitor with the intent to stay and adjust status....except for a K-1. Any discussion to condone or instruct others in illegal immigration activities of any kind is a violation of the terms of service for Visa Journey. Coming to the US as a visitor with the intent to marry and leave is fine......but intent to stay and adjust status is not....regardless of whether it is 30 days, 60 days, or 90 days. If an attorney tells you otherwise, run away.
Having said that, if a person entered the US with the intent to visit, then their situation changes, it is legal to marry and adjust status (proving the marriage is to a US citizen). Waiting 90 days has no advantages. In fact, it could endanger the beneficiary.