Okay, first, big {{{{{hugs}}}}}. I can totally relate. The only fight DH and I have ever had that resulted in DH storming out of the house and leaving for hours happened over DS's bed time.
At some point, after tons of obsessing, I made this my sleep motto: "It's just sleep, not Godliness." (Secular version: "It's just sleep, not virtue.") That is to say, your big goal for your child's life is not that he be a fabulous sleeper, but that he grow up to be a person of virture and character. Sure, it would be nice to get some sleep along the way, but in the big picture, what we want for our LO's is so much more than that.
I seriously wrote that motto on a big piece of paper on DS's door 'cause it helped me keep perspective. I know it's hard when you're so tired.
TBH, if you're paying for your consultation with Ferber's nurse, I'm really reluctant to advice you to do anything other than what she says, kwim? I'm guessing it's making your DH crazy that ya'll are paying for that and you're coming and getting conflicting advice from us, yes?
If she weren't in the picture, I'd probably encourage you to keep it the same for a few more days and then start to slowly, very very slowly, decrease his A times, making his night 10.5 hours. From a BW perspective it's all about listening to cues and if he's seemed to need 13.5 hours of sleep, and he's acting very tired before bed time, I'd want to make tweaks to accomadate those things.
TBH, I'd do with his routine whatever is best for your marriage right now. If that means sticking with the nurse's advice, that's what I'd do.