If you have your green card and a valid Brazilian passport, you may travel at any time.
The processing times for green cards depends on the anchor relationship used to obtain the visa number. The Department of State controls the number of visas issued each year based on the type of relationship and your country of chargeability. If you are married to a U.S. citizen and present in the U.S. pursuant to a lawful admission, CIS generally issues the card 6-9 months after you apply. If your sibling petitioned for you, the visa may not be available for many years.
Please consult with an immigration attorney prior to engaging CIS.
Processing times for Green Cards vary, depending on the facts of each individual case, and whether the case was properly prepared and documented. Always use a qualified immigration lawyer when dealing with the USCIS. The problem cases that take years are usually done by people trying to do it themselves and not understanding some of the simple principles required for a successful application. Remember, it is not enough to just complete the forms and submit them, there are other nuances in form and procedure that need the attention of a specialist, no matter how simple it may appear on the Internet.