I have a 2-count misdemeanor (dui + high BAC) on record from 3 years ago. Does "clean" period start AFTER probation ended?

While a simple DUI/DWI offense by itself is not a crime involving moral turpitude, this can be complicated by any elements of the offense(s) involving intent or knowledge, such as driving with a suspended license, reckless driving, driving with a child in the car, etc., so you should meet with an immigration lawyer to review the specific charges under state law, and all the underlying facts and circumstances of your case. The facts and the sections of law charged should be reviewed in detail before even deciding whether to file for citizenship or wait until 3 yrs/5yrs after the end of the probationary period.

Any DUI/DWI within the statutory period is not a situation where an applicant should ever file an N-400 without legal representation. Some naturalization officers at USCIS district offices around the country will treat a DUI as a disqualifying offense regardless of the state charges or the underderlying facts, and that will be an incorrect application of the law in certain cases, so anyone in this situation should get a lawyer to assist them in applying for citizenship. In some cases, the answer will be that you have to wait. In others, you may be able to file, but do not look for an analysis of all your specific facts on the Internet: consult with a qualified immigration attorney and provide them with the actual Certificate of Disposition for any charges, whether or not you were convicted, and tell the lawyer honestly about what happened that led to the charges - no attorney can advise you properly if they are not aware of all the facts.

This is general information only. It is not intended as a substitute for legal advice, and does not create an attorney-client relationship.

Karin Wolman is right. You were lucky to find such a thorough and knowledgeable review here.

Typically probation for these offenses is three years. If you complete probation without violation and are not facing any new charges, you are entitled to have the original charges dismissed. This requires a petition to the court. Even if you have violated probation, you can petition the court to have the charges dismissed. The decision when you have violated is within the discretion of the court.