It could take over a week. Some strains(i think this is not common in modern commercial strains) grow a very thick seed shell that you might need to help open a bit, either very gently cracking the seed open(i usually use my teeth) or by sanding the side where the seed opens with fine sanding paper. But i think this is more of a problem with northern landrace strains and crosses made from them that are bred outdoors.
I think best method is to put them in a glass of water with a drop of some root nutrient stuff, then when they open and show a beginning of a root, put them between wet paper towel for like two days until the root is half inch to an inch and then put it in soil or cube so that the tip of the plant is nearly on the surface or just on the surface if root is inch or longer. Also you can put it in a bit larger hole, so that you can easily bury some of the stem as it grows.