Thanks for your query.
The timestep on the output hydrographs is controlled by the timestep of the temporal patterns written into the storm file. Thus, unless you rescale the temporal patterns to be expressed on a shorter timestep, RORB will not produce hydrographs on a shorter timestep.
If you require hydrographs on a shorter timestep in a hydraulic model, the best approach is to manually interpolate these in a spreadsheet or other means outside RORB.
Having said this, I’m a little surprised that your hydraulic model requires input hydrographs at a certain timestep. Most of the major hydraulic models (eg HEC-RAS, MIKE, Tuflow) I am aware of will do this interpolation for you automatically.