Sorry I had logged off right after I responded before. I would actually have the opposite advice, I find that I have the best success rate when I get them in soil as soon as the seed cracks, the longer you wait and the more tail there is, the bigger the chance of it getting damaged/contaminated and dying off. Those little tails are really an internal organ, and they are very delicate. I also plant them an inch, inch and a half under the soil so that it travels through enough medium to knock the shell off, when they get above ground and the shell is still covering the cotyledons the chances of survival start dropping, at least in my experience. Also, don't be surprised if it takes longer than you expect for it to pop, I've had seeds take almost 2 weeks to pop after being put under soil, I had totally counted them out but kept watering anyways and they came up and really took off, it just means the plant is putting down a longer root before pushing up above the soil, so don't give up on it if it hasn't broken soil after a few days.