IIRC, Frozen Turkeys take 24 hours per 5 lbs of bird to defrost
Given that a butt is a hunk-o-meat, I would allow a little extra time for complete defrost.
I'd allow 3-4 days before you want to smoke one, take it out of the Freezer, and place into the Fridge.
If it was not vacuum-packed, I'd...