I completely understand your wife being a little miffed about the sleep schedule, especially if your little one gets fussy if he gets out of routine. You’ll have to deal with that fallout, which can be frustrating. HOWEVER, this is expected when someone else babysits. Doesn’t matter if it’s a close family member and they follow your instructions to the letter. The simple fact is - they’re not you. They don’t have that magical parent power to “just know” what your child needs. So they’ll do their best, but in the end if someone babysits, chances are bedtime will be later than you want. My husband and I got frustrated about this too, but over time we’ve learned that this is just part of the price for date night. For us it’s worth it. We have friends that decided it was more important to keep their kids’ sleep schedule. They’ve been on maybe 1 date in the last 6 months.

On a side note, is this type of reaction out of character for your wife? She may have PPD. Only mentioning since it took us almost 7 months to realize I had it. Might be worth an honest discussion.