I never tried to germinate the seeds. I had an entire hill of Japanese maples, dogwoods and azaleas. Every year, I would go through the 1000's (literally) of baby JM's looking for the good ones. The promising ones were potted and the rest pulled up. None of them were ever Moon maples.
When I have germinated JM's on purpose, I have potted them up and let them sit outside for the year. They always come up in the following spring. If I were to stratify them in the refrig, I would leave them for several months to mimic what they would get outside. That's my whole strategy whenever I germinate any seed - mimic what would happen outside.
You belong to a Bonsai club? How fun is that? I took lessons years ago and also learned a lot from my father in law.
I have only kept a couple bonsai - the ones ok with this climate.
The tiny ones are too labor intensive so I given those all away. I have a couple in training (Ume', an oak and some Pinion Pines) but the only ones I have left are in 2 - 5 gallon pots. I always start with seedlings, never the 'chop and there you have it' bonsai.
My oldest is about 45 years old - a pot of ginkgo.