The ancient Goths had a custom of debating twice: once drunk, and once sober. Mr. Shandy didn't drink, so he eventually hit on a modified version of the custom: once on the first Sunday night in a month, and once on the night just before it. (Remember what the Shandys do on the first Sunday of every month?)
Mr. Shandy calls these his "beds of justice," because he's a boss like that. Tristram has his own way of settling tricky spots in his book: he writes full and corrects while he's hungry, or the other way around.
This way, he finds a middle course and writes a careless kind of a civil, nonsensical, good-humoured Shandean book (6.17.8).