Sage (herb) is classed perennial 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
Start seeds indoors
8–6 weeks before the median last spring freeze
Wisconsin Horticulture says to start sage indoors 6 to 8 weeks before the average date of last frost, so sowing runs 8 to 6 weeks before the last spring freeze.
Transplant outdoors
from the median last spring freeze to 2 weeks after
UMD Extension names sage among herbs started indoors and planted outside after the danger of frost has passed, which coincides with Wisconsin Horticulture's direct-sow date, so the window opens at the last spring freeze.
Direct-sow outdoors
from the median last spring freeze to 2 weeks after
Wisconsin Horticulture gives a point rule — plant sage seed directly in the garden on the average date of last frost — which opens a two-week sowing span beginning at that date.
Variety assumption: Wisconsin Horticulture notes seed-grown sage may not flower the first year; culinary leaf harvest is unaffected.