Approximately speaking, what is the smallest temporal difference, expressed in milliseconds, in note lengths (for consecutively sounded notes) that an average, untrained listener can still (semi)consciously perceive? What order of magnitude are we talking about here? 10 ms? Or more like 50 ms?
In order to make the question a bit easier to answer, let us confine our attention to the following situation: a diatonic scale of quarter notes, played slightly legato on a concert grand, in a slow adagio-like tempo (60 BPM), and in a room without any noticeable reverb.
I'm trying to quantify the "infinitesimal" lengthening and shortening of notes going from one phrase to the next, but I find it difficult to come up with realistic numbers.
Edit: I'm not asking for the shortest perceivable note duration, but for the smallest perceivable difference in length between two consecutive notes.