Planck time

A unit of time in an absolute system of units devised by Max Planck, about 5.391 24 × 10⁻⁴⁴ second. Symbol, t_P. Algebraically, it is

$the square root of a fraction. hG is the numerator. c to the fifth power is the denominator.$

where c = the speed of light, G = Newtonian gravitational constant, and ħ = the reduced Planck's constant.

From the equations, you can see that a velocity of 1 Planck length per Planck time is the speed of light.