The stock market is behaving curiously.

Or maybe not.

Matt Levine, whose daily Money Stuff newsletter from Bloomberg is wonderful, made an interesting observation about the market’s behavior during the coronavirus crisis in today’s edition (scroll down to the third story).

Stock indices have fallen a bunch in the last month, but it turns out that almost all of that fall happens in the first five minutes of the trading day. The general pattern is that futures trade limit-down after the close of the market, and stocks generally follow suit by trading limit-down at the open, triggering a circuit breaker and halting trading for fifteen minutes so everyone can gather themselves.

And then something kind of weird happens: The rest of the trading day, on average, is up slightly from the plunge that tripped the breaker. Did people spend the entire night freaking out, and then turn that panic into losses at the open, only to be calmed by a fifteen-minute break at 9:04am?

He cites another study that, during the preceding bull market, most of the upside in the market happened at the start of the trading day, and performance flattened for the remainder. Folks have speculated that that’s a sign of some kind of sinister manipulation. But it’s the same effect, essentially, in a mirror-image market: All of the move at the open.

Levine makes a different suggestion: Maybe people spend the hours when the market is closed reading and thinking. Right when the market opens, they do the thing they decided to do overnight. Then, for the rest of the day, they sort of hang out.

If that’s right — I bet folks are looking into it — it would support another proposal that Levine has made. We could shorten the trading day to be just a couple of hours long. Not clear that a workday trading floor hours from back when there was an actual wall at Wall Street, and people convened under a buttonwood tree to swap paper, makes sense anymore. A brief opportunity to trade equities every day might be just as effective as a longer day.