Am I understanding correctly that ALL 2D output is written to the plan .hdf file (e.g., .p##.hdf)? Is the 2D output written at the computation interval? Is there any way to change the interval at which 2D output is written to the plan .hdf file?
I dont think thats possible. But remember "Mapping Interval" is not just for the visual representation in RAS mapper. For example if you run a d(t) of 1 second but map at 3 minutes....if you check your output hydrographs or structure hydrographs or flow over a weir, it will only have data at the "mapping interval" for which you have defined.