Well -- you should plant the seeds as soon as the taproot emerges. The taproot is the lifeline and is fragile - so it should be moved to its permanent home ASAP after emerging, so that it can continue to grow, and the plant can begin to thrive. As for how long do you wait for a seed to germinate if it doesn't pop? Your call. Some seeds are not viable, and will never crack - some take longer than others. I have seen some discussion about "Fresh seeds" and whether or not they should be frozen prior to atttempting to crack them -- to simulate the winter months that would occur between the time the seed was created, and the following spring when the seed would be best to crack.
If they don't crack after 2 days there is a good chance they are not going to. This does depend on the conditions as well - it will take them longer to germ under less than ideal conditions. Under ideal conditions, they will crack in 12-24 hours most of the time - under poor conditions, it may take as long as 2 weeks. Fresh seeds contain inhibitors that prevent them from germinating well - this is a survival method. You don't need to freeze them (in fact one should NEVER freeze seeds it causes cellular damage which lowers the germ rate) but if you wait a few months to pop them they will be fine. Chickadee's got it right though - they are very fragile at this stage and should be planted as soon as the tap root emerges. Be sure to check them at least every 12 hours and transplant them ASAP.
You are going to send people into an absolute panic!!!!! Do you know how many people post in this forum about seeds taking too long to crack --- and you're going to tell people that it takes 12-26 hours for a seed to germ? and then on top of that you're going to tell people that if they don't germ in 2 days - they aren't going to? shame.
If the seeds are good and they are in a proper environment (85-90 F and high humidity) that is all it takes. If you are not getting them to crack this quickly then either you are not storing your seeds right or you are not germinating them in an ideal environment or you are using crappy seeds. This is subjective of course - it can take much longer for them to crack if the environment is not ideal. If you just throw them outside in a pot in early spring of course it will take much longer maybe even a week or two. I usually get about 50%-70% popping within the first 24 hours and the other 20% - 30% or so withing the next 24 hours, as do most of the experienced growers I know. It is very rare that it takes any longer that that but there are exceptions. However, most people are probably not as anal with their storage and germination methods as I am which makes a big difference. Also a lot of the seeds floating around out there are pretty crappy even those from seed companies - it helps considerably that I am extraordinarily picky about my genetics and where they come from.
Yeah I don't really agree....I believe it was...well some guy said if you give it enough time it will grow. Now, I had 4 seeds germing and 3 crack in like 2 days...the 4th didn't crack for about 4 days. I almost...ALMOST chucked that seed down the drain cause I though if it didn't crack it wouldn't, than I remembered that saying and left it alone a little longer and low and behold...I have 4 sprouts.