The guidance I have read is not clear to me when converting a business from reporting as self employment to an S Corp what date(s) are available to make it effective.

If the client sets up an LLC, effective July 1, 2023 and immediately files Form 2553 to elect treatment as an S Corp, can the 2023 tax year be split Jan to Jun as SE income and Jul to Dec as Sub S income or does he have to wait until the following year, January 1, 2024, to start being taxed as an S Corp?