What is the standard SI unit for time?

The story behind the answer

Second is correct because the SI (International System of Units) defines the second (s) as the base unit of time. Other familiar time units are derived from it: 1 minute = 60 seconds, 1 hour = 3600 seconds, and 1 day = 86,400 seconds.

Modern science defines the second very precisely using atomic physics: it is the time it takes for 9,192,631,770 oscillations of the radiation associated with a specific transition in the cesium-133 atom. Atomic clocks based on this keep GPS, telecommunications, and scientific measurements synchronized worldwide. Memory tip: Think “SI = Second Is standard,” and remember that minutes, hours, and days are just convenient multiples of the fundamental scientific unit.