If you are filing Form I-751 jointly with your spouse, you must file it within the 90-day period before your conditional residence expires.
In some cases, the marriage may have ended due to divorce or death. It may also be possible that the marriage is still valid, but it is impossible to file jointly because the conditional permanent resident is abused or battered. In these rare cases, it is possible to get a waiver of the joint filing requirement. You may file I-751 at any time when filing with a request that the joint filing requirement be waived.
If you have failed to file before the expiration of your conditional green card, you have lost your permanent resident status and may be removable from the United States. CitizenPath recommends that you immediately contact an experienced immigration attorney that can assist you.