Note: A rough approximation of the time step you need for an InfoSWMM or H2OMAP SWMM model can be found by finding the mean link length using the field statistics tool for the length in the Conduit DB Table and then estimating the time step from the mean length, mean full depth velocity and mean full depth wave celerity.
The time step actually used during the simulation is related to this velocity and the safety adjustment factor. The larger the safety adjustment factor the larger the mean time step listed in the Routing Time Step Suggestion.