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 Time Scale is the estimate of a star's lifetime based upon its nuclear fuel and the rate at which fuel is burning, while its Thermal Time Scale (or Kelvin-Helmholtz Time Scale 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 is the time scale for Gravity to pull the mass of a body together.
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.
Chemical Equilibrium (CE)
Final Parsec Problem
Type Ia Supernova