Can go upto the validity period...
Just because you have applied for 485 does not mean that you cannot have any vacation. Lawyers are unnecessariliy frightening people. The assumption here is that when you are away from US on AP, the 485 process is supposed to be in suspension. But that never happens. Either the processing takes so long that your travel goes unnoticed or the IIO is not concerned with AP usage and gives the approval.
Even if your 485 is approved when you are away, you will be allowed in AP and will be asked to go to the local INS within a specified date since they will stamp your AP with deferred inspection.
You can always show that you had 2 different events scheduled at your home country (or whereever you are going)and that is why you had to be away so long (and do not volunteer this info. say it only if asked about the long stay).
FYI myself, my spouse, my many friends have been in AP for time upto 2-3 months. An officer at POE said the general guidance is upto 3 months for them to inquire as to why you have been away for a long period time while on AOS.
Of course this is my opinion.