Well I never did know that…
a unit of time used in computer engineering. A jiffy is the length of one cycle, or tick, of the computer’s system clock. In the past, this was often equal to one period of the alternating current powering the computer: 1/60 second in the U.S. and Canada, usually 1/50 second elsewhere. More recently the jiffy has become standardized, more or less, as 0.01 second (10 milliseconds). The word jiffy, with its ordinary meaning of an instant or very brief time, appeared in English during the eighteenth century, but its origin is not known.
a unit of time used in chemistry and physics, equal to a “light centimeter,” that is, the time required for light to travel a distance of one centimeter. This is a very brief interval indeed, about 33.3564 picoseconds. This definition of the jiffy was proposed by the American physical chemist Gilbert N. Lewis (1875-1946), who was one of the first to apply principles of quantum physics in chemistry.
Taken from : http://www.unc.edu/~rowlett/units/dictJ.html