>> those with harder seed coats would require more time for the coat to soften and crack
After losing 90% of my first 2-3 sowings of snow peas every year, I read a suggestion to Deno-spout peas on paper towels! Then plant the sprouted peas as soon as a few millimeters of root have emerged. I'm going to try that with early snow peas and snap peas this year.
Maybe it would also be a smart way to start "scratch and soak" seeds like lupins.
I have a healthy respect for microorganisms. It's often a close race between seeds rotting and rooting.