Is now a good time to plant maple seeds? I've collected some Japanese and trident maple seeds to experiment with but wasn't going to plant them until June-ish.
Storing for a couple of months will not affect the viability so June or July would be fine to sow. They can also be sown now and left to nature. That seems to work for the trees and they have been doing it for millions of years. Make sure your seed trays are protected from rodents. Any rats or mice in your area will be sure to find any accessible seeds and they will all disappear before spring.
I normally get mine into the fridge around mid June and plant them out around 12 weeks later.
I have not grown maple seed in warmer climes but fridge is certainly not needed in this area. Stratification may help with older, stored seed but my experience has been mouldy seed when I tried fridge stratification. I hear that disinfecting with bleach or peroxide helps reduce mould on seed.
My experiments with grafting have not really been aimed at bonsai because grafts are usually so obvious. Grafting is just to give the seedlings a chance to survive long enough to assess the characteristics and see if it might be a viable landscape type. I have also been trying different grafts to see if I can find a satisfactory method and location where grafts will not be obvious for bonsai. That would allow us to grow some of the varieties that are so hard to propagate on their own roots.