Transient heating with ns pulse of the absorbed power

I want to monitor transient heating of the sample which is absorbing a power from FDTD simulation during 30ns. I understood that I have to use global monitor shutter, with the step function, so I have changed my steady state simulation by choosing:
shutter mode: pulse on
shutter ton [fs]: 1e+06
shutter toff [fs]: 31e+06
shutter tslew [fs]: 1e+06.
and it fails. What should be min time step and max time step in this case? Should I change other parameters?

The min time step should be at least 1e6 (fs) or less to properly model the pulse. The max time step could be much larger (say 1e10 fs). You would want to make the max step size larger because the thermal time constant is usually in the order of millisecond so a large max step size is required to speed up the simulation. This large mismatch in the time scale (between the thermal constant and the pulse width) will make your simulation very challenging as you will need a small step size to model the pulse but then that will require a huge number of time steps to finish the simulation which will probably run a few milliseconds.