[mathomp4]

Summary

• Make standalone FV3 setup Milan-only at NCCS ahead of Cascade Lake retirement; preserve NAS Cascade Lake support.
• Set C12 and C24 timesteps to 1200 seconds to match the standard GEOSgcm_App horizontal-resolution defaults.
• Override the timestep to 450 seconds for L72, matching the GCM's default L72 configuration without introducing a microphysics dependency.
• Leave processor layouts and other resolution-dependent settings unchanged.

Validation

• Compared the extracted FV3 timestep block with GEOSgcm_App/set_resolution_params.csh using tcsh: all 44 combinations of 11 standard resolutions and L72/L91/L137/L181 matched the corresponding GCM defaults.
• Checked intermediate-resolution timestep ranges.
• git diff --check passed.
• Full experiment generation, model stability, and NCCS job submission were not tested.