If you in fact have advanced parole (look at the card very carefully) then you can stay out for a year. Keep in mind that even if you have advance parole, you should consult with an attorney to make sure there's nothing in your immigration history that would complicate your return since when USCIS issues advanced parole they don't check your eligibility to return.
The information offered is general in nature and not meant to be relied upon as legal advice. Please consult an attorney prior to making legal decisions. Visit us at www.tunitskylaw.com. Contact us at 713.335.5505 or email at firstname.lastname@example.org. Veronica Tunitsky offers in-person, as well as telephone and email consultations.
I do not recommend a long trip. Also consider that if the I-485 is denied while you are away, you will not be paroled in.
This response is general in nature and cannot be construed as legal advice, given that not enough facts are known. Any comments offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship. If you would like additional information based on this response, please contact my office at 510 657 7665 or 415 902 0832 to schedule a consultation.