Rutabaga (cool-season root vegetable) is classed hardy in the cited extension guidance. The timing rules below are relative to your local freeze dates — enter a location to turn them into calendar dates.
The rules this site applies
Method
Frost-relative window
Rule & reconciliation
Fall planting
100–86 days before the median first fall freeze
University of Illinois Extension says "For fall harvest, plant rutabagas about 100 days before the first frost," a point rule that opens a 14-day sowing span 100 days ahead of the first fall freeze; UGA Circular 942 agrees the crop is frost-anchored ("2 ½ to three months before a heavy frost") but ties itself to a heavy frost rather than the first 32°F freeze that this engine uses as its anchor, so the Illinois wording — which names the first frost directly — was the one encoded.
No direct-sow outdoors window: Illinois Extension states a frost-relative rule only for the fall crop ("plant rutabagas about 100 days before the first frost"); its spring sentence covers turnips rather than rutabagas, so no spring window is computed here.
Variety assumption: Assumes a standard 90-day variety such as American Purple Top or Laurentian grown as a fall crop; Illinois Extension notes rutabagas need about four weeks longer than turnips, which is why only a fall window is encoded.