If you received a notice of abandonment, then you must file the petition no later than 2 months from the mailing date of that notice. If you did not receive the notice of abandonment, then the deadline for filing the petition is 2 months from the date you learned of the abandonment, rather than two months from the mailing date of the notice of abandonment.  However, this more lenient deadline will only apply if you were diligent in prosecuting the application.  To be considered diligent, you must have checked the status of the application every 6 months since the filing date of the application.