Datura has a mind of its own .. some start germinating a few days after you plant them and others can take weeks even months. Through many years of growing datura I've found a way that works very well for me. Using cuticle scissors, which are very sharp and bowed, I cut a sliver off the edge of the seed (see picture for which side to use), just enough to break through the coat using the bowed side .. no more than that, then plant them about 1/4 inch under soil. I start all my seeds on heating pads and keep the soil in the upper 70's to low 80's. For most seeds, I usually have germination within a week or two .. super fresh seeds usually come up in a few days.
I use the Deno method since these seeds can take up to 1 month to germinate. I soak them first in hand hot water over night to plump them up.
Tear a sheet of kitchen paper towel. Use 1/2 of it. Fold it over twice. Wet it, then squeeze out the excess moisture. Open one fold and place your seeds inside. Fold one side over the seeds and place the package in a ziplock baggie. Zip up to 1/2" and blow into to it, then quickly zip it close. The air will remain in and prevent the seeds from being squeezed between the plastic.
Place the baggie in a warm place---top of fridge or heat mat. After 3 days begin to check seeds every day. As soon as you see sprouts, plant it. Be sure to aim the rootlet downwards. I use a tweezer to hold the seed. Some seeds will sprout within a few days, other will take longer. The beauty is that if you regulate how many plants you want instead of wasting seeds. Just sow a few more of the numbers you want.
Here is a thread I started from my own experience on over winter Datura in the fridge.