For filing Form 5472 and the pro-forma 1120 for your LLC, if for example it was created on June 1, 2026.
Tax period: from June 1, 2026 to December 31, 2026. This is a 'short tax year' because it lasts less than 12 months.
Filing deadline: April 15, 2027. This date applies because your short tax year ends on December 31, 2026, which places you in the category of filers following the calendar year. The general rule for these filers is to file no later than the 15th day of the 4th month following the end of the tax year, hence April 15.
Extension (Form 7004): by filing Form 7004 before April 15, 2027, you obtain an automatic six‑month extension, pushing the deadline to October 15, 2027.
Filing by mail: your statement is correct. The complete package (pro‑forma 1120 + Form 5472) must be sent by postal mail.
Address to use: Internal Revenue Service, 1973 Rulon White Blvd, M/S 6112, Attn: PIN Unit, Ogden, UT 84201.
Proof of delivery: it is strongly recommended to send your package by certified mail with return receipt. This will provide you with proof of timely filing.
Important note on the form type
Since your LLC is a disregarded entity owned by a foreign person, you must write 'Foreign‑Owned U.S. DE' (or 'Foreign‑Owned Disregarded Entity') at the top of the first page of the Form 1120 you attach.
I recommend that you have these steps performed by a US‑based tax professional. You can find this type of service provider on Upwork for about $600.
Furthermore, it is strongly recommended to keep accounting records for your LLC in case of an audit.