Planck Time Is How Long It Takes Light To Travel One Planck Length
What's the tiniest length of time you can think of? Maybe milliseconds come to mind. Try again, but this time think like a physicist. Physics uses units of Planck measurements, which are extremely tiny. The Planck time is the smallest conceivable length of time. Its definition might make your head spin: One unit of Planck time equals the time it takes light to travel a distance of one Planck length in a vacuum. Keep in mind the Planck length is the smallest conceivable length.
German physicist Max Planck, the founder of quantum theory, proposed Planck units in 1899. They were invented, as reported by Universe Today, as a "means of simplifying the particular algebraic expressions appearing in theoretical physics, especially in quantum mechanics." Getting back to Planck time specifically, here's an easier way to imagine just how small it really is: There are more units of Planck time in one second than all the seconds since the Big Bang. Learn more about Planck time in the video below.
What Is The Shortest Possible Unit Of Time?
Could anything be shorter than Planck time?
from Sixty Symbols
Key Facts In This Video

1
The Planck length is the smallest length (it measures 1.61619926 × 10^35 meters). (0:01)

2
The shortest possible time may be the Planck length divided by the speed of light. (0:28)

3
The attosecond may be the shortest amount of time that has ever been identified. (1:00)
The Planck Length Is The Smallest Length At Which SpaceTime Functions
It's way smaller than a proton.
Planck's Constant
Learn the origin of quantum mechanics.