Scheduling a change in the time step of a simulation

Hi to everybody.
I'm running a transient simulation using AMS Simulator.
The simulation consists in long periods in which the voltages and currents of the circuit remain unchanged, alternated with short periods in which they vary quickly.
The point is: to have a good resolution in the short periods, I have to set a small time step for the simulation; but this way I use a small time step for ALL the circuit, and the simulation takes a lot of time.
My ideal solution would be to have the possibility to schedule a change in the time step during the simulation.
In the AMS Simulator manual I read that with the function OPTION one can set scheduled changes for some simulation parameters, but not for the time step.
Any suggestions?
Thanks a lot,
Emmanuele