second picture of full tree

If you are in DC proper, than you are probably past frost, but I wouldn't say "safely" past, as there have been later last freezes as recently as 2007. If you are in the suburbs, the average last freeze ranges from April 10th to April 20th. Just FYI.

Yes DC proper, in a dense urban neighborhood. But your right, I'm not planting my vegetables yet because a frost is still possible.
That said, is the possibility of frost a significant consideration in transplanting the JM? Is the current growing stage risky or advisable for transplanting?

Generally speaking, late autumn or winter, when the tree is dormant but the ground is not frozen, is best for transplanting. Its obvious from the photos that the tree is starting to come out of dormancy. You could definitely get away with it, but for highest odds of success, it would be best to wait until next dormant season.

Not too late at all but do it quickly!! "Last frost" date has no bearing on planting or transplanting hardy woody plants - that term is used only in reference to cold sensitive plants like annuals or tender perennials.

As a gardener with a lot of Japanese maples, I would not hesitate to move a tree that size at that stage of seasonal development. Your risk factor is about nil.

i would be more concerned with a sudden heat wave .. rather than cold...

this weekend at the latest ...

ken

It sounds like you might could use some tree planting advice! Take a look at the information at the link below. Section 1 covers planting times, but I'd recommend you read the whole thing carefully. Frost dates are not mentioned because, like Gardengal said, they are irrelevant.

Here is a link that might be useful: Planting a Tree or Shrub