Cucumbers (warm-season vine crop) is classed very 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
Start seeds indoors
2–1 weeks before the median last spring freeze
Sow in individual pots 3–4 weeks before the outdoor window opens (UNH 3–4 weeks; Missouri G6570 3–5 weeks, sown directly in pots).
Transplant outdoors
2–4 weeks after the median last spring freeze
UNH allows setting out 1–2 weeks after frost; Purdue's very-tender class (at least 2 weeks after) is the more conservative and is used.
Direct-sow outdoors
2–4 weeks after the median last spring freeze
Purdue: very tender — sow at least two weeks after the average last frost (UNH adds: when soil reaches 70°F). Penn State's earliest sowing (May 11 for a May 1 frost) is slightly earlier; the later Purdue rule is used.
Seed germination soil temperature: optimum 95°F (optimum range 60–95°F); minimum 60°F, maximum 105°F. Purdue HO-186-W Table 3. Cold soil below the minimum rots seed — a reason windows and soil readings both matter.
Variety assumption: Assumes an average slicing variety (about 55–70 days from seed; Penn State lists 70).
Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.
Earliest/latest sowing dates for a May 1 last-frost / Oct 1 first-frost baseline; offsets derived by date difference from May 1. Also days-to-maturity figures.