Hello!
I don’t have any personal experience with it, but this is what it says on USCIS site:
What if I am Late in Applying to Remove the Conditions on Residence?
If you fail to properly file the Form I-751 (Petition to Remove the Conditions on Residence) within the 90-day period before your second anniversary as a conditional resident, your conditional resident status will automatically be terminated and the USCIS will order removal proceedings against you. You will receive a notice from the USCIS telling you that you have failed to remove the conditions, and you will also receive a Notice to Appear at a hearing. At the hearing you may review and rebut the evidence against you. You are responsible for proving that you complied with the requirements (the USCIS is not responsible for proving that you did not comply with the requirements).
The Form I-751 can be filed after the 90-day period if you can prove in writing to the director of the Service Center that there was good cause for failing to file the petition on time. The director has the discretion to approve the petition and restore your permanent resident status.
