You apply for a waiver of the Joint filing requirement, you need to provide evidence that you entered the marriage on good faith.
You can file the I-751 anytime after a divorce or annulment has been finalized, you do not have to wait until within 90 days or the green-card expiration.
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Filing after Divorce or Annulment
A conditional permanent resident with a marriage that was terminated due to divorce or annulment must file for a waiver of the requirement of the joint filing of Form I-751. To obtain an approval of the I-751 and be granted unconditional lawful permanent resident status, the conditional permanent resident spouse must be able to show that s/he entered into the marriage in good faith.
The person seeking permanent resident status should expect to undergo an interview at the USCIS about the marriage. The USCIS will closely scrutinize whether the marriage was bona fide at its inception. The USCIS will review the divorce decree and complaint for matters that may be reflective of whether the marriage was entered into purely for immigration purposes or to perpetrate fraud against the United States citizen spouse or the USCIS.
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