An SCorp election effective date is the date the election to be treated as an NY SCorp went into effect from the filing of NY Form CT-6 (Election by a Federal SCorp to be Treated as an NY SCorp).
An SCorp first files to be treated as an SCorp on with the IRS Form 2553 (Election by a Small Business Corporation). Line E of Form 2553 indicates the tax year the election will take effect. See sample screenshot of the 2553 form below.
Here is more information within the instructions of filing the NY CT-6 form. (See sample screenshot attached.)
Approval of election: You will be notified whether your election is approved, and if approved, the date the election will take effect. Until then, do not file Form?CT?3?S or CT-32-S. If you are now required to file Form CT-3, General Business Corporation Franchise Tax Return, CT-4, General Business Corporation Franchise Tax Return Short Form, or CT-32, Banking Corporation Franchise Tax Return, continue filing it until your election takes effect.
Years for which election is effective: The election will be effective for the entire corporate tax year for
which it is made and for all succeeding tax years until terminated.
https://www.tax.ny.gov/pdf/2014/corp/ct6i_1014.pdf
