They can sprout in 2 weeks or 2 months. I've had seeds from the same pod germinate at very different times. Being that you are in zone 5 it might be a bit late but you don't have anything to loose. Put the pot someplace warm and wait. Since the others molded so quickly they might no longer be viable.
Karyn

Datura seeds do have odd germination periods. I just had a D. ferox seedling come up from a pot that I haven't touched for five months. I find that Datura thrives best (and flowers earlier) when it has a lot of space to spread its roots, and is just a little be parched for water. Then again, I've seen Datura plants along streams that have shown amazing growth. For me, though, they don't like to cooperate unless I create conditions which put a little stress on them while giving them room to grow.

Interestingly, I also find that Datura wrightii and Datura inoxia, when grown in close proximity in a pot, will abandon long taproots in favour of many small roots. It makes them much easier to transplant than the monsters that I dig out of the ground. I spend a couple of hours chasing a single tuberous root through a big pile of mulch, and ended up finding a network of potatoes and a sprouting avocado pit.

But yes, the seeds might take some time to sprout. Datura metel does this to me often, so I wouldn't discount the seeds' viability for at least a couple of months if I were you.

How fun....so if they sprout, I should consider them a houseplant until next year huh? Right now the pot is on the deck getting some natural heat.