Planck scales is a definition relating to what is possible for us to measure. "One Planck time is the time required for light to travel, in a vacuum, a distance of 1 Planck length."

"In physics, Planck units are physical units of measurement defined exclusively in terms of five universal physical constants listed below, in such a manner that these five physical constants take on the numerical value of 1 when expressed in terms of these units. Planck units elegantly simplify particular algebraic expressions appearing in physical law.

Originally proposed in 1899 by German physicist Max Planck, these units are also known as natural units because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are only one system of natural units among other systems, but are considered unique in that these units are not based on properties of any prototype object, or particle (that would be arbitrarily chosen) but are based only on properties of free space. The universal constants that Planck units, by definition, normalize to 1 are the:

Gravitational constant, G;

Reduced Planck constant, ħ;

Speed of light in a vacuum, c;

Coulomb constant,

Boltzmann constant, kB (sometimes k).

Each of these constants can be associated with at least one fundamental physical theory: c with special relativity, G with general relativity and Newtonian gravity, ħ with quantum mechanics, ε0 with electrostatics, and kB with statistical mechanics and thermodynamics. Planck units have profound significance for theoretical physics since they simplify several recurring algebraic expressions of physical law by nondimensionalization. They are particularly relevant in research on unified theories such as quantum gravity.

Physicists sometimes semi-humorously refer to Planck units as "God's units". Planck units are free of anthropocentric arbitrariness. Some physicists argue that communication with extraterrestrial intelligence would have to employ such a system of units in order to be understood. Unlike the meter and second, which exist as fundamental units in the SI system for (human) historical reasons, the Planck length and Planck time are conceptually linked at a fundamental physical level."

It may not be the 'smallest' scale possible, but it also has to do with how you define 'reality'. Under Plank scale all classical definitions breaks down, and SpaceTime as we know it 'disappear'. And as we live in SpaceTime I would call that pretty special.

And that's also where our arrow should start to behave weirdly as I think of it.