When would be the right time to transplant a few maple trees?
Right now is the perfect time. Anytime from mid fall to early spring is good.
Dig your hole at least twice as wide but not quite as deep as the tree's rootball. Ideally, the top of the rootball (the top of the highest root) should rest just slightly above the surrounding grade when planted. If planting a nursery grown tree, check to ensure that the tree wasn't planted too deep in the container. A bowl shaped hole is best.
Don't add amendments to the fill dirt. Use only the soil you removed from the hole. Amendments frequently cause drainage issues and root growth problems.
Examine the tree for circling roots. Sometimes nursery grown plants are replanted in larger pots with circling roots intact. This will lead to root girdling as the tree ages.
Mulch the planting site at least as far out as the hole you dug. Farther out is better. If you use hardwood mulch or small bark chips, about 3" is a good depth. Mulch should not be placed up against the trunk. Leave a couple of inches right around the trunk unmulched. I taper my mulch down closer to the tree and mulch a little closer for aesthetics. Mulching adjacent to the trunk can lead to trunk rot, contribute to disease issues, and give cover to rodents that might like a bite out of your tree. "Mulch volcanoes" should definitely be avoided.
I'm thinking about saving these instructions and adding to them as needed, so if they are unclear or you can think of something I didn't cover, please let me know.
The trees are just across the road from where I live. I will be digging them up myself. Still see no problems with doing it before the leaves fall?
No. The dangerous time to move a tree is in late spring or in summer months. During these hotter periods transpiration rates are higher than a partial root system can support. You won't have to worry about that now. Getting the trees in the ground now will give them the maximum time possible to get established (regrow the lost part of their root system) before the stress of hot summer months.
An added advantage of doing it now is you can choose for fall color.
We have good sugar maples, and we have some maples with very similar leaves that don't turn color, that just hang on as dead brown leaves. Avoiding their offspring is a necessity.