A final determination of Automated Traffic Law Violation liability shall occur following failure to pay the fine or penalty after a hearing officer's determination of violation liability. Where a person fails to appear at a hearing to contest the alleged violation in the time and manner specified in a prior mailed notice, the hearing officer's determination of violation liability shall become final: (a) upon denial of a timely petition to set aside that determination, or (b) upon expiration of the period for filing such a petition without a filing having been made.