"It is comparatively easy to measure the thresholds that our brain uses to create temporal structure, i.e. the minimum time interval required to correctly tell apart the sequence of brief sounds or images," he writes--that's measured in the milliseconds.
But temporal integration, which refers to combining sensory information and creating the sense of a subjective present or the perception of a "now," is trickier to evaluate.
It can't really be measured, at least not with our currently available methods and understanding, but "many observational studies point to a three second rule of temporal integration in the brain."
One of those studies "involved the analysis of poetic meter."
The short version of Rehman's essay: three seconds may be an important temporal unit for our brain.