According to the Reference Manual of Woody Plant Propagation, you can either stratify for 3 months at 40 degrees, or plant as is and expect to take 4 months for germination. Al

With fresh seeds (aril removed and planted approx. two weeks of harvesting) I had 1 in 3 germination and it took 3 and half months indoors over winter months (October '10 to January '11). I have some seedlings emerging even now - that is 6 months. I am in the UK so same hardiness zone as yours probably. Seeds were given a gentle file with a nail filer and planted 1 cm deep in multipurpose compost mixed with sand and grit. They were watered well and then covered with cling film over the top and left on a bright window sill. I didn't try any seeds direct outdoors. I watered sparingly if the compost looked dry.
So may be you need to wait. Hope this is of help.

jinginuk: Good to know, that helps a lot. No germination for me yet, but it has been just over 2.5 months or so for the ones indoors. I have been remiss on keeping the humidity and moisture levels high for the seeds, so I do not expect them to germinate after all - but you never know.

How is the growth rate of the seedlings for you after germination?

Worthwhile to wait and see - best of luck.
The stem of the seedlings measures between 3 to 4cm with healthy leaves (4-6)on top. Once the seedling hit the cling film I put the pot into a plastic bag tied at the top but still on the window sill as it was wnter. My impression (just 2nd time I've tried growing a tree from seed) was that they seemed to grow to 4 leaf stage quite fast and then slowed down. I have recently moved them out to an unheated greenhouse as there was a short spell of warm weather. But it has gone cooler so I think they might slow down even more as that's their permanent home now.