They are not yet ripe so unlikely to be very viable. Japanese maple seeds ripen in the fall, typically late September into October.

Sorry, but they do not ripen once they are pulled off the tree.

Here's a pretty informative link on growing JM's form seed. It is important to know exactly what you get when you grow from seed....and they are not named cultivars :-))

Here is a link that might be useful: growing JM's from seed

I'll bet that 'lovely' nursery appreciated you stripping the seeds off their trees for sale.......
Don't come to my garden.
Mike

Please ignore "Mike's" post. We all learn as we continue the art of gardening.. The link offered is a genuine respected gardening site.

If you would like I have a great site for purchasing a wide variety of different Japanese Maple seed. It will be important for you to do some research so they will be grown in the correct zone. I live in zone 5a, but with winters that are too mild, it creates a difficult situation for growing any type of JM. Lets do our homework and maybe together we can come up with a inexpensive way to propagate JM seed.

I think the OP should heed Mike's post. Removing any part of a plant from a nursery, public or private garden without permission is akin to stealing. That means any seeds, seedheads, flowers or snips/cuttings and is just not an accepted thing to do.

And it is important to acknowledge that "a wide variety of different Japanese Maple seed" will still only get you a generic Japanese maple.

Thanks Pam.
I'm wondering how a winter in Zone 5 Colorado Springs can be too mild for Japanese maples.
I grow hundreds of seedling Japanese maples, and yes, they are unnamed generic Japanese maples. I'm not selling them so they don't need a name. I just plant them in my garden.
Here are some of the red ones I'm trialing out.
Mike

Here is a link that might be useful: Fall in my garden

I hadn't thought of occasional warm spells in the winter causing the maples to break dormancy. That can be tough!
Thanks kmattie61.
Mike