Are you saying you will be filing the "late election" to be taxed as an S-corporation for 2024?
If so, first, verify that you qualify for the election.
Second, one of the requirements for the late election is that once you realize you forgot to file the election on time, you have "diligent actions to correct the mistake upon discovery". In other words, file the election NOW.
Third, one of the requirements for the late election is that you thought you were being taxed as an S-corporation and were acting like it. That means you file the extension as an S-corporation, not a C-corporation. If you file as a C-corporation, you would be indicating you were NOT acting as an S-corporation and would NOT qualify for the late election.
If you meant you'll be making the S-election for 2025 (or a future year) and will be filing as a C-corporation for 2024, just ignore my prior comments. 🙂
