gnasa

I'd like to weigh in and offer my experience that may give some insight to OP.
My AU wife adjusted status (from F-1/student to GC) back in 2010. I was subsequently transferred for my work to Europe ~4 weeks after GC arrived. We ultimately obtained a re-entry permit (REP) a little less than 1 year after the transfer (I've posted another thread detailing why the delay). Essentially my wife was out of US for ~11 months without an REP and we entered TOGETHER without any issue. We ultimately received the REP which is valid until here conditional GC expires. ~8 months later we had another trip to the US. Even when armed with valid GC and REP (and new baby, joint US-AU citizen) border officer sent her to 2ndary processing and was quite rude to me when asking a simple question if I and baby should accompany my wife to the next 'station' (ah my wonderful tax dollars at work - entry at Boston Logan). Wife was admitted without any issues as her LPR is maintained and has a valid REP.
It is clearly a gamble as to the 'quality' of the border agent you encounter. They can make the experience very unpleasant but have little authority to actually take the GC away, that can be only done by a judge. There seems to be an unwritten 6-month rule that border agents follow - that is absences of <6 months = little suspicion LPR has abandoned residency, >6 months = reasonable suspicion LPR has abandoned residency, >1 year without REP = abandoned residency (this is written).
I think OP shouldn't have too much difficulty entering country with LPR spouse after 5-6 months provided they have some financial/social/business evidence that they 'intend to reside within the US permanently'. Eliminate 'visiting' from your vocabulary and replace it with 'staying in touch with friends/family' or 'attending job interview' or 'evaluating home purchase', don't lie but LPR needs to tailor responses carefully if scrutiny is applied. It's clear that in no way are you trying to get around GC requirements, life sometimes takes a little time to move to another country and USCIS sometime understands this.
Disclaimer - I'm not a lawyer, just a laymen trying to balance career & family & interests with global opportunities.

Hi Little My,
I think I can offer you some advice by sharing my experiences... I'm a US citizen and my wife currently has a conditional GC and we moved to Europe ~4 weeks after she received it due to my work transfer. We ultimately obtained a re-entry permit (REP) (it's a long story, search my user name for threads with addition details) and I highly recommend you obtain one in your hands before you depart.
The #1 first thing you should do is get a REP, even if you don't plan to be out of US for >1 year. This 1st REP will most likely be valid for 2 years or until the date your GC expires, whichever is earlier, in your case it sounds like the conditional GC will set this date.
Why you should do this: As I understand it, USCIS cannot use the time during a valid re-entry permit to count against you in their consideration of abandoned residency. It also is a strong demonstration that your travels abroad are temporary and you do not intend to live abroad permanently. A REP does not protect the time required for naturalization/citizenship, but if you're worried of possibly deemed to have abandoned residency a REP is a part of your insurance.
When entering the US my wife has on her

joint US tax returns for several years
scan of our vehicle title that we left in the US at my mom's house
scans of some recent US credit card bills (we use one of my US family's house as the billing address)
scan of marriage cert.
print outs of relevant USCIS communication
REP
GC
and the newest development, a US citizen daughter!

We've had no problems so far entering the US.
In addition, it may possibly be easier to enter if your US husband is with you. Go through the same line and step up to border agent together. We answer any questions truthfully, honestly and efficiently without offering additional information. I don't want to oversimplify it, but if the very very worst happens and USCIS takes your GC (which is extremely unlikely if you have a valid REP), then you do have the right to obtain another one.

Another short answer is yes. It is possible to do an early walk-in at a separate facility than listed in the biometrics appointment notice, but it's not guaranteed. And it wont affect the timing of your processing.
As with many processes in USCIS, unfortunately it depends on the day and mood of the USCIS employee (in addition to schedule constraints). I suggest you try an early walk-in somewhere in the Eastern US. To accomplish this 1) I would research on here when are the better days to try 2)when at facility be clear, nice, and well organized/justified/presented (e.g. bring your plane tix showing you'll be in Eastern US during scheduled biometrics appointment), and it may just work out for you.
See thread: 'Re-Entry Permit: Applied After Departure' for a success story that did just what your contemplating.