They have a habit of pusing up out of the plug and growing a really short taproot, this happened twice on this grow... be sure that you get them to the bottom of the hole, or take stinky's advice, you get better contact with the plug that way.

All 7 of my seeds popped in 24hrs and had roots showing through the bottom by the end of day 3.

Also, be sure that you get them in their medium solidly, if you're using hydroton (like me) they're not too solid and they move around alot if you're not really careful.