If you are applying based on 5 years as a Permanent Resident or 3 years as a Permanent Resident married to a U.S. citizen, you may file for naturalization up to 90 days before you meet the “continuous residence� requirement. For example, if you are applying based on 3 years of “continuous residence� as a Permanent Resident married to a U.S. citizen, you can apply any time after you have been a Permanent resident in continuous residence for 3 years minus 90 days. You may send your application before you have met the requirement for “continuous residence� only. Therefore, you must still have been married to and living with your U.S. citizen spouse for 3 years before you may file your application. You must also meet all the other eligibility requirements when you file your application with USCIS.
disclaimer: i am not a lawyer, this is knowledge from my own expirience.
