Most seeds will germinate anywhere from 36 hours to 12 days. However, if most of your seeds have germinated, and a few which were started at the same time remain unchanged, then you may want to scuff these. The most likely reason that these seeds have not germinated when the others have is due to a thick shell, which the seedling cannot break through. When it fails to do this, water will not be able to penetrate the shell and therefore allow the seed to grow.
To safely thin the shell, line a small box (such as a matchbox or concentrate container) with sandpaper. Place the seed or seeds in the box and shake it thoroughly for 2 or 3 minutes. Once you have done this, place them back in the soil, rockwool or paper towels and they should be able to germinate much easier in a few days. If for some reason this method does not work, you shouldn’t bother trying to continue germination as it likely means they will not turn into a desirable plant.