Sinking indicates full (100%) absorption. Immediately after sinking, dissolved oxygen (DO) levels within the embryo begin to decrease.
In wild environment, the natural wet/dry cycles of sunrise/sunset; dews, rains, and evaporation within the top inches, all contribute to periods of wetness followed by periods of dryness. The cannabis seed is apt at surviving rather low moisture concentrations for prolonged periods of time; while is more prone to rot and drowning.
Its my suggestion that after soaking in cup of water–if the seed has sunk indicating absorption, while the casing has yet to crack and no taproot is exposed–to allow the seed 10 minutes of air drying before re-planting into moist media; be it soil, coir, rockwool, etc.
One reason why paper towel method seed germination techniques see such success for new growers, is that a higher quality paper towel (or more layers to increase transdermal absorbency) permits a constant wicking effect, which when sealed in a bag or between plates, creates a pseudo-terrarium effect and perpetually cycles the moisture immediately surrounding the seed, always bringing fresh D.O. to the seed (slowly through the cycle of evaporation and wicking).
I personally throw cannabis seeds on the surface of the cup of water and allow them to float until I observe the first sink. Consider that corn and soybeans are the largest commercial seeds and require some of the longest soak times. Farmer’s Almanacs as early as the 1880s recommend soaking corn seed for no less than seven hours; other crops, typically four or fewer hours. (edit: Old almanacs also recommend soaking corn for no more than 24 hours to avoid “rot”.)
It is my opinion that regular grower habit is to over-saturate cannabis seed stock, and that the greatest improvement to germination results over time is garnered from knowledge of the leverage of a natural wet/dry cycle in seed development; once adequate moisture is present to start the seed, oxygen then becomes the limiting factor; when more rapidly supplied, the embryo more rapidly develops.
I’d get the sunken ones dried off (10mins) and planted.
Thanks for sharing your progress in this, and best wishes! I’ll surely follow along in appreciation =)