ohnosecond

from The Free On-line Dictionary of Computing (8 July 2008)

ohnosecond

   <unit, humour> (Presumably a play on "{nanosecond}") The
   miniscule time it takes to realize that you've just made a BIG
   mistake like typing rm -rf * in the wrong directory.

   Seen in Elizabeth P. Crowe's book, "The Electronic Traveller."

   (1998-08-27)