The Lyapunov Time of a dynamical system is the
Timescale over which it is chaotic.
The Lyapunov Exponent is its inverse.
Some calculated examples:
solar system  50 million years 
Pluto's orbit  20 million years 
Kepler 36  3000 days 
(physics,dynamics,mathematics,chaos,timescale)
http://en.wikipedia.org/wiki/Lyapunov_time
