Except as otherwise provided in this section, an effective premarital agreement is void 18 months after the parties to the agreement become parents or guardians of a minor. The premarital agreement is not void if, within the 18-month period, the parties sign a written amendment to the agreement either stating that the agreement remains in effect or altering the agreement. Sections 607 and 608 apply to any amendment under this section.
This section does not apply to premarital agreements executed on or after October 1, 1993.