reducing simulation time with LENGTHENING_STEP
Starting from a swmm model with 31 subcatchments with a total area about 126 ha, 460 joints, 58 km conduits and 1 rain gage with one year of ten minutes precipitation data, it takes above 4 hours to calculate. Changing the LENGTHENING_STEP from 0 to 10 there was a significant reduction of computational time. After that I test simulations of a day and iteratively resolve issues related to timestep-constraining locations. Following this steps the simulation time has been reduced from 4 hours to 4 minutes. Thank you very much to Mitch Heineman for all his good advices.