There is not a hard rule about how much time to spend on each phase, but I've found that by starting at ca. 200 K, heating and initial thermal equilibration can usually be accomplished in about a nanosecond. (Note that Langevin should NOT be used during heating.)

General system equilibration is not so easily defined; I generally monitor time series for a number of properties such as potential energy, radius of gyration, backbone dihedrals, etc., to look for evidence that a steady state has been achieved, which can easily take a hundred or hundreds of nanoseconds. The details of the specific system are a major factor, with larger and more complex systems requiring longer equilibration times.

Rick Venable
computational chemist