You're obviously filing the I-751 based on an exception that allows you to file with evidence of a bona fide marriage that has/will be terminated by divorce. Technically speaking, that application does not need to be filed before the 2nd anniversary and can be filed up until the government tries to remove the person. Having said that, I try to file these within the 2-year window anyway because no one wants the govt breathing down their neck. What happens generally is that USCIS will give you an extension while your divorce is pending (since they can't approve the petition until the divorce is final). All this can be tricky and I advise you to get some help.
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You should consult with a immigration attorney like myself before you do anything that may SEVERELY jeopardize your case. If you can not come to the office I offer consultations over the telephone. A denial of that application may subject you to removal proceedings.
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