what is too slow for germination?

Sometimes seeds do take up to a week to crack open. It has probably used a lot of its energy cracking open But since your seed already has a root it will definitely grow. This seed might take a few extra days to grow its main tap root. But once the seed sprouts and starts producing its own energy it will grow like a normal plant. Give it time and patience. The seedling stage is the worst for my patience as well. Go ahead and place it in soil. Give the tap root a faster time to decide which direction is down and it'll pop up the fastest this way. No need to let it grow further and lose more energy in the napkin.