What you’re talking about sounds similar to the Planck length to me. I’m not a string theorist, but my understanding is it is well defined in normal 4D spacetime (where Planck time would be the time it takes a photon to travel one Planck length). Planck length is based only on universal constants (Planck’s constant, speed of light, and the gravitational constant), and so any “thing” smaller than that is unphysical.

I think the interesting question is how do we get continuous experiences, measurements, and observations from a spacetime that is fundamentally quantized.