Lima Bean (warm-season vegetable) is classed tender 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
Direct-sow outdoors
from the median last spring freeze to 2 weeks after
Illinois Extension's Hort Answers entry for Phaseolus vulgaris and P. lunatus says beans should be planted after all danger of frost is past, and Utah State's legume planting guide places the warm-season legumes — which it lists as snap or dry beans and lima bean — around the frost-free date; both point to the last-frost date itself, so the point rule opens the window at the anchor and runs the standard 14 days. Illinois' allowance for planting a week to 10 days early in warm soil was rejected as the earlier-starting, less frost-conservative reading.
Variety assumption: Assumes bush or pole lima sown directly in place; Maryland Extension notes limas need soil at 65°F for five days to germinate well, so gardeners in a cold spring should plant toward the later end of the window rather than at its opening.