The updated policy, which comes into force on November 1, 2018, states that the Form I-693 must be signed no more than 60 days before the applicant files the underlying application for which Form I-693 is required. The validity of the form is more closely tied to the timing of the underlying application. The Form I-693 would remain valid for a two-year period following the date it was signed.
This change in policy will allow USCIS to avoid delays in adjudicating the underlying applications since there will be fewer requests for updated Forms I-693.
From personal practice, I would like to point out that although the Form I-693 was good for 2 years, immigration officers in the vast majority of circumstances required applicants to update the form if it was a year old.