When To File

When my wife got her green card, I could have sworn that I was told to file her Petition to Remove the Conditions of Residence 6 months before her green card expired, but reading the I-751 application, it says "you must file it during the 90 days immediately before the second anniversary of the date you were accorded conditional resident status.", I understand this as it has to be 90 days or less before the green card expires. Am I understanding this correctly?