I'm doing some work on key press handing in a firmware project. I've been googling to try to find what the typical duration of a key press is, particularly the minimum for a fast typist. Surprisingly I can't find any figures for this anywhere.
There are some recent studies on keypress timings that have published there timings. Here are two:
http://www.cs.cmu.edu/~keystroke/ (Data gathered by Kevin Killourhy and Roy Maxion as accompaniment to "Comparing Anomaly-Detection Algorithms for Keystroke Dynamics").
Pressure-Sensitive Keystroke Dynamics (Gathered by Jeffrey D. Allen as part of his thesis).
In summary, these studies give values roughly between 50mS and 300mS.