If you plan on being absent from the United States for longer than a year, it is advisable to first apply for a reentry permit on Form I-131. Obtaining a reentry permit prior to leaving the United States allows a permanent or conditional permanent resident to apply for admission into the United States during the permit’s validity without the need to obtain a returning resident visa from a U.S. Embassy or Consulate abroad. Please note that it does not guarantee entry into the United States upon your return as you must first be determined to be admissible; however, it will assist you in establishing your intention to permanently reside in the United States.
Morales Law Firm P.A. 2100 Coral Way Ste 703 Miami, FL 33145 (305) 851-7856 This response is not offered as legal advice, but is only a general informational response for public interest. No one reading this is authorized to claim that an attorney client relationship exists with this writer or the writer's law firm.
6 months is the most you can be absent safely.
Do not believe the rumors you have heard about being able to use a re-entry permit for 24 months ... there are great risks with doing it that way ... especially if you have only recently become an LPR.
There is no such thing as a 36 month permit.
FORMER IMMIGRATION LAW PROFESSOR -- LEGAL DISCLAIMER: This answer is offered for informational purposes only. It does not constitute an attorney-client relationship.