depending on how big it is already you should be able to plant straight out, just be sure not to put in windy locations or frost pockets. very hardy trees!

Mine in England is sheltered from the worst of the winds and has survived for about 15years with the lowest temps of around -15centigrate and the high 20's c in the summer, occasionally late frost turns some flowers brown

Don't know how this compares to your growing conditions

I would say outside, and, as others have said, in a sheltered spot out of the worst of the wind.

Be careful not to disturb the rootball when planting - magnolias do not like root disturbance

Thank you so much for all your responses. I really do appreciate the help.