Ryan, 1 year and 9 months after your wife adjusted her status (when you went to the BCIS agter you were married) is the first day you can apply for the I-751. Ray is correct in that you have a 90 day window to apply for this. They will not accept the application any earlier than 1 year 9 months and if you apply after the 24 month deadline you have to send additional paperwork as to why you did not file on time.