arsenic hour
n. The time after parents arrive home from work and before dinner is served; any extremely hectic part of the day, especially when dealing with young children.
It's almost dinnertime. Mom or Dad, or both, are trying to get dinner going. They've just arrived home from work or they're reeling from a long day of parenting. They're tired, the kids are wired and everyone is hungry. Among other things.

Let's peek inside one household:

The oldest child has a million questions and an attitude. The middle child needs a hand in the bathroom. The baby wakes up cranky from his afternoon nap. Then he poops. The dog, who has some issues of his own to work out, has decided to pick this particular moment to have a meltdown. He starts scratching the paint off the door and then begins barking as if a serial killer is in the house. Simultaneously, the cat relieves itself in an unauthorized location.

The best that can be said about the above situation is that it's not my house. Our only pets are fish, who are usually very polite and well-behaved, particularly if you drop an occasional mention of "fillet" as you pass by the tank. The children are another matter. This is the time of day known as "the arsenic hour." Why? Because you either want to dispense some arsenic or take some.
—Bill Lohmann, “Arsenic Hour,” The Richmond Times Dispatch, March 22, 1998
1975 (earliest)
Between the nap and the twilight
When blood sugar is becoming lower,
Comes a pause in the day's occupations,
That is known as Arsenic Hour.
—Marguerite Kelly & Elia Parsons, “The Mother's Almanac I,” Main Street Books, September 24, 1975
After I'd been researching this phrase for a while, I found out that it appears in a book from 1975 (see the earliest citation), which would normally make it too old for Word Spy. However, by then I'd already come across a huge number of synonyms: rush hour, witching hour, sour hour, hurricane hour, granny hour, scotch hour, sherry hour, and suicide hour. Clearly there's a deep well of black humor that's the source of these terms. Arsenic? Suicide? This forces those of us who are childless to wonder just what on earth is going on out there?

In neological circles, the presence of a large number of synonyms for something usually means not only that that something is an extremely common phenomenon, but also that it doesn't have an official name. (The sociological term for arsenic hour is the forgettable and far too understated transition time). Given the apparent intensity of the experience, people feel a need to label it somehow, so they come up with X hour constructions modeled, no doubt, on phrases such as rush hour and, ironically, happy hour. (Although see children's hour, below.) So in the end I decided that arsenic hour was post-worthy because it's a linguistic reflection of what appears to be a significant, or at least commonplace, cultural phenomenon.

Note, too, that the earliest citation is clearly based on the Henry Wadsworth Longfellow poem, The Children's Hour (1863), so arsenic hour was originally an ironic play on that phrase:

Between the dark and the daylight,
When the night is beginning to lower,
Comes a pause in the day's occupations,
That is known as the Children's Hour.