AP can be issued (and is normally issued) to aliens who have a pending I-485 who wish to travel abroad. While the application form states that it is for "emergent personal or bona fide business reasons", it has regularly been used for non-emergent travel abroad with little or no problems. Besides, what constitutes "emergent" and how does USCIS determine it? So the "emergent" requirement has more or less been ignored by immigration officers. After all, if AP was only for emergency, why would USCIS have issued
this statement a while ago? There is an entire thread about this
here (long but interesting).
On the other hand, AP can also be applied for if you have a foreigner who normally lives abroad who you need to bring into the US immediately for emergent reasons and who cannot wait for visa processing times. It must be a real emergency (e.g. US citizen dying and needs to bring foreign sibling ASAP), and cannot be used "to circumvent the normal visa issuing procedures and is not a means to bypass delays in visa issuance". This type of AP for foreigners abroad is what this last sentence is referring to, and not to I-485 applicants wishing to leave.
In all cases, there is no actual
rule about time limits on staying abroad other than returning before the expiration of the document. Whether the immigration officer suspects that your center of life is not in the US and wants to make a big deal out of it is always possible I suppose, even though you are technically supposed to maintain your center of life in the US
after you obtain your green card.