Giorgio,

You could have also edited the time steps in the SWMM GUI window and entered 00:00:05, for example, as the Routing time step in SWMM 5. You always enter the time in HR:Min:Sec as it says at the top of the GUI dialog. It was not necessary to edit the *.inp file to make this change. I snipped a little of the output file to show you the general format for time in SWMM 5.

****************
Analysis Options
****************
Flow Units ................ CMS
Flow Routing Method ....... DW
Starting Date ............. 06-04-1979
Starting Time ............. 00:00:00
Ending Date ............... 06-04-1979
Ending Time ............... 12:00:00
Wet Time Step ............. 00:15:00
Dry Time Step ............. 01:00:00
Routing Time Step ......... 00:00:05
Report Time Step .......... 00:00:10

Best Regards,
Bob Dickinson
DickinsonRE@CDM.COM