I realize an S-Corp needs to file their tax return "by the 15th day of the third month following the close of their tax year".  

If an S-Corp revokes their S-election on 1/31/2025, then their final short-year S-Corp tax return would be due on 4/15/2025.  What if the S-Corp revokes their S-election on a day that is not on the last day of a month.  For example, if the revocation date is 2/17/2025 or 2/21/2025, what is the due date of the short year S-Corp tax return?  Is the third month May, regardless of the February closing date (with the return due on 5/15/2025)?  Or is the third month based on the actual end of business date (for example, if the closing date is 2/17/25, then is the return due 15 days after 5/17/25)?