The term Timescale or Time Scale is used for the rough length of time something takes. In astrophysics and Cosmology, time scales are modeled for various phenomena regarding stars, star systems, orbits, planets, galaxies, etc. Timescales of competing or concurrent processes are compared to see which match observation.
For example, in stellar theory, the Nuclear Timescale is the estimate of a star's lifetime based upon its nuclear fuel and the rate at which fuel is burning, while its Thermal Timescale (or Kelvin-Helmholtz Timescale or KH Timescale, or for short, Kelvin Time) is an estimate of its lifetime based upon the idea that its radiation was fueled solely by cooling. Free-Fall Time (or Dynamical Timescale) is the time scale for Gravity to pull the mass of a body together, ignoring other forces.
The fact that stars' observed actual lifetimes match the nuclear timescale rather than the thermal timescale was evidence convincing astronomers that Main Sequence Stars run on nuclear energy.
Similarly, for clouds, a Cooling Timescale is the time scale for a gas cloud to cool (based on its gas's Cooling Function), and the comparison of this and the Free-Fall Timescale is a means to represent the results of the two tendencies.
Chemical Equilibrium (CE)
Final Parsec Problem
Type Ia Supernova