USA Two quick questions related to Single Member Tennessee LLC Taxed as a C-Corporation

[Nichecities]

1. My LLC was formed in December of 2018. It's currently taxed as a C-corporation. We're using a Fiscal Year End of September 30th for tax purposes.

Note: This is where I'm really confused. No article has been able to explain this succinctly:

What is my fiscal year allowed to be legally?

Would it be December 2018-September 30th, 2019 and then just Sep 30th, 2019 to September 30th, 2020 and so on and so forth (September 30th, 2020 to September 30th, 2021)?

2. When is my federal tax return due?

Correct me if I'm wrong, but it would just be the 15th day of the 4th month following my fiscal year end so 1/15/2020?

 

[KrashTax]

You must fill out form 1128 to request a change in tax year for a C corporation. The IRS requires you ask for a "Ruling Request" on this form as part of its criteria to approve a fiscal year change. Mail your completed form 1128 to the National IRS office at: Internal Revenue Service Associate Chief Counsel, PO Box 7604, Ben Franklin Station, Washington, D.C., 20044-7604. Ask for a ruling request if you are not eligible for automatic approval. Attach form 1128 to your amended return. if approved your first tax year would be December 2018-September 30th, 2019

yes its the 15th day of the 4th month.