3/15 is the last day to file for 2020. the IRS will notify you that either it was accepted for 2020 or will be effective next year. can be mailed or faxed see filing instruction on page 3 of the instructions for the form.
https://www.irs.gov/pub/irs-pdf/i2553.pdf
some may point out that a late election can be filed but there must be a reasonable reason why it was filed late.
