Yes, there is - Planck time, which is the shortest possible duration, and is in effect an instant, but is of measurable, though vanishingly small, duration. The spacial equivalent is the Planck length, effectively a point. I'm not a physicist, so if I've misunderstood this, put me right, anybody, provided you know what your talking about, and preferably without the sarcasm which seems to be de rigeur on this forum.
Simplistically, the Planck units are an exercise in
dimensional analysis. Basically it's a set of units based on what are considered to be fundamental natural constants; speed of light, Planck constant, gravitational constant, etc. instead of our invented standards for mass (kg), time (s), length (m), and so on. The equations that define the Planck units are simply the ways in which you can combine the physical constants so that the answer has the units you want. Hence, the Planck time is given by
t
p = sqrt(ħG/c
5)
Where ħ is the reduced Plank constant, G is the gravitational constant and c is the speed of light. It's worth noting that dimensional analysis ignores dimensionless (unitless) constants, so there's nothing to tell you whether to use (for example) the Planck constant or the reduced Planck constant, that differ by a factor of 2pi.
The exact physical significance of the Planck time depends on how general relativity and quantum mechanics combine, which is currently unknown. It is true that hypotheses that quantise space-time (e.g. Loop Quantum Gravity) do regard the Planck time and length as the size of the relevant quanta and this is often repeated as if it is fact.
The Planck time is way beyond our ability to measure.