https://www.vice.com/en_us/article/g5bx8j/scientists-clocked-the-shortest-time-period-ever-247-zeptoseconds

Scientists have clocked the shortest time measurement ever, expressed as 247 “zeptoseconds,” during an experiment that probed one of the most basic encounters between light and matter.

A zeptosecond is equal to a trillionth of a billionth of a second, making it one of the tiniest units of time known to science. Even shorter timescales exist in theory, such as the cosmic constant called Planck time, but these units are so exotic that it is not yet possible to measure them in a laboratory environment.