Several times I have read here to wait until spring when leaves are starting to swell out from training, with good reasons.

In the edition of International Bonsai from William Valvanis theremos an article by Isaburo Nishiyama reprinted from Bonsai World 1984 which says, "In the mild climate of Japan the time to restyle Japanese maple is in the autumn, immediately after the tree drops it's leaves. Winter pruning in January will cause ugly cuts to remain."

The article never mentions roots, but talks about cutting branches. I would not think of Japan as mild but his advice seems to conflict the advice from the highly experienced folks on Bonsai Empire.

I have three Japanese maples outside which just lost their leaves two weeks ago. They are destined for a group planting. Should I rush right out and put them in the pot, or should I wait until March or so?

Ivan Mann wrote: SI would not think of Japan as mild

Really? It does have a tropical rain forest climate so that seems quite mild to me.
Or a humid continental climate with long winters.

Guess it depends on which region you're taking about (climate zones: en.wikipedia.org/wiki/Geography_of_Japan#Climate_zones )

I'm nog great with maples. I would not touch them in winter, apart from pruning branches - which I recenly did. Personally, I'd not repot them now.
But again... I'm not to great with 'm so do not take my advice for granted.

repot at spring don't prune now