savetime was just an example. You could use saveclock or saveperiod too.
saveclock is in WALL time not simulation time. It cannot be less than a second - so setting saveclock to 100n will not do anything (saving the state every 100ns of real time would be infeasible). If you set it to 60, it would save every minute (even that is probably too frequent).
If you want every 100ns of simulation time, use saveperiod=100n.
These both work - I just tested them.