K, I just planted three different strains each with a good sized tap root and two of them popped up within 36 hours. On the third day I did some digging and found seed #3 still underground and trapped in the shell. I gently removed the shell and it's now growing and should survive, though it's looking a bit rough. Based on past experience 3 days is my limit before I investigate, as the cotyledons will rot if they can't get exposed to air and light. This latest seed of mine would have definitely been gone for good had I waited much longer. So if your seeds already had a decent tap root showing when you planted them 3 days ago, you should probably take a look-see. Very (very!) gently and slowly take a toothpick and remove the soil a tiny bit at a time. You will find one of three things:
1. Plant has shed the shell and is heading to the surface. If so, keep it uncovered until it grows taller and then backfill the soil.
2. Plant is trapped inside the shell but roots seem to have grown down into your medium. If so, gently (gently!) attempt to pry the shell off without damaging the plant inside. Sometimes I can do this with a toothpick and sometimes it takes a pair of tweezers. There also may be a brownish membrane that needs removing, and that is even more delicate work. If you do this and the plant inside looks yellow and dead, don't give up because I've had them come back to life quite well. Give it a couple days and it may green back up.
3. Tap root is dead and/or the plant sprouted and then went black and slimy. If so, germ another seed. It happens to all of us.
Just my "My 2 cents" after dealing with this situation many times over the years. Also note that this applies only to seeds planted with the tap root already exposed and growing. If you are just putting seeds in the soil before they crack open, it could take a week before they sprout.
i pop in when i can see how you doing 
