What it does to the argument

There's a cost that lands on the row itself, and it's worth separating out, because a couple who argues badly at midnight can come to believe they argue badly, and they don't. They argue at midnight.

The late argument is a worse argument than the same argument would be at any other hour, and worse in specific ways. It escalates, because Anderson and Platten's finding is that tired people hold back less with negative things, and the sentence that would have been thought and not said at eight is said at half past twelve. It circuits, because chapter 11's fourth point isn't available and the three that are get restated. It pulls in everything, because the late brain can't hold one subject and the thing from March is nearer the surface than it would be at breakfast. And it's misremembered, because what each of you takes upstairs at one is the worst sentence of the night rather than its substance, and the misremembering is what the next row opens with.

The morning argument is about the thing. The dishwasher, and what the dishwasher was standing for. It has the fourth point in it. It's had a night's reprocessing, in Walker and van der Helm's sense, so the charge is lower and the content is clearer. It's ten minutes long, because ten minutes is how long a row about a dishwasher takes when the two people having it can think. And it ends, in the sense of finished rather than exhausted, because finished is available at eight.

Same couple. Same dishwasher. Same disagreement. Two arguments, and the hour is the only difference, and the hour is the thing the old rule fixed at the worst possible place.

People who move their rows to the morning say the same thing, in my observation, which is that they'd thought they were bad at arguing and it turned out they'd been arguing at one in the morning. They weren't bad at it. Nobody's good at it at one. The argument you'd have at eight is the one that shows you what the two of you are actually like when you disagree, and for most couples it's a relief to find out.