The SI Unit for time is the second. The second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.
In other words, a second is an extremely precise measure of time that allows us to keep track of very small intervals. For example, modern atomic clocks are accurate to within one second in about 300 million years!
The SI unit for time can be used to measure any interval or duration – from seconds to months or even years. It’s also useful for measuring frequency (the number of times something happens per unit of time). For instance, we can use hertz (Hz) to measure how often a machine operates – like how many cycles per second an engine is running.