24-Hour Stock Trading Is Booming – and Wall Street Is Rattled

Wall Street pros are feeling uneasy about retail investors again. Only this time it’s not about the trades they’re making — it’s about when they’re making them.

The amateur-investing revolution that has swept US markets since the pandemic is helping fuel a boom in overnight stock trading. It’s playing out at the likes of Robinhood Markets Inc. and Interactive Brokers Group Inc., which have adopted ways to offer the buying and selling of American shares 24 hours a day, five days a week.

That has effectively eliminated the traditional eight-hour overnight break, and the move has proved so popular that others are taking note. Even the infamous “pink sheet” market — ...