Early autumn ideally.
Peonies aren't fond of being moved but as it's still a young plant you might get away with digging it up now but take a big block of soil with it not just the rootball - and be prepared for it to sulk while it settles down again.

Agree with Urbanite, best time to move, if you must, is early autumn. Do it now and the tree peony will sulk for far longer… they purely 'hate' being moved at all!

I moved mine last Autumn and thought I'd killed it. All the branches fell off. Miraculously it must have shocked it into blooming this Spring for the first time in 3 years. It needs to be planted deeper than ordinary peonies.

thanks, everyone...since i do have to move it before the fall, i'll be careful to take a big hunk of soil...maybe if i talk nicely, it will forgive me!..............pat

Could well do…

For future reference, the ideal time to move a paeony is immediately after leaf fall.

thanks, Andrew...that's good to know...i had numbers peonies in my old garden, but never needed to move them..