When it's dormant, normally - but be careful not to plant it if your soil is frozen.

Which species, Angelina, and about where in the States are you?

A miniature Magnolia! that's a new one to me ..

I'm thinking that it is probably one of the dwarf varieties of M. grandiflora, such as 'Little Gem', or 'St. Mary's'. Since I don't know, I asked! : )

Be interesting to see a photo :o)