About 4 ns at an ion density of 10^20/cc. If you assume no magnetic field effect, given the measured ion temperature, the electron temperature should have risen in that time to 19 keV. But the measured electron temperature peaked at 3.6 keV.
Actually, since the magnetic field effect makes ion heating of electrons far les efficient than elctron heating of ions, it allows a steady state difference in ion and electron temperatures of as much as 20 to 1. This is calculated from very standard physics and no laws of thermodynamics are violated.
