I don't know where you got that date (2/29), but the NY instructions for Form IT-204-LL says: You must file Form IT-204-LL and pay the filing fee in full on or before the 15th day of the third month following the close of your calendar or fiscal tax year. For calendar year filers, that's 3/15 not 2/29. Here is a link to the instructions:
https://www.tax.ny.gov/forms/current-forms/it/it204lli.htm
