From https://www.irs.gov/instructions/i2553#idm139855003296080

Item E. Effective Date of Election

.Form 2553 generally must be filed no later than 2 months and 15 days after the date entered for item E. For details and exceptions, see When To Make the Election and Relief for Late Elections, earlier..

A corporation (or entity eligible to elect to be treated as a corporation) making the election effective for its first tax year in existence should enter the earliest of the following dates:

When the corporation (entity) is making the election for its first tax year in existence, it will usually enter the beginning date of a tax year that begins on a date other than January 1..

A corporation (entity) not making the election for its first tax year in existence that is keeping its current tax year should enter the beginning date of the first tax year for which it wants the election to be effective.

A corporation (entity) not making the election for its first tax year in existence that is changing its tax year and wants to be an S corporation for the short tax year needed to switch tax years should enter the beginning date of the short tax year. If the corporation (entity) doesn’t want to be an S corporation for this short tax year, it should enter the beginning date of the tax year following this short tax year and file Form 1128, Application To Adopt, Change, or Retain a Tax Year. If this change qualifies as an automatic approval request (Form 1128, Part II), file Form 1128 as an attachment to Form 2553. If this change qualifies as a ruling request (Form 1128, Part III), file Form 1128 separately. If filing Form 1128, enter "Form 1128" on the dotted line to the left of the entry space for item E.