The next 12 hours, from midday to midnight, are called pm. However, you can tell the time without saying am and pm. To do this you can use the 24-hour clock. The 24-hour clock always uses 4 digits.

Some of those traders are used to how trading in futures, FX and other markets work, where they offer trading outside U.S. working hours, sometimes 24 hours a day. As the U.S. stock market moves ...