Curing concrete can give up moisture for a very long time. You can check it after a couple of weeks by putting a piece of plastic over it, and see if any moisture is accumulating on the plastic. IIRC, on one job we used a heat lamp shining through the plastic to accelerate the evaporation. If there are any doubts about it still giving out water vapor, you might set the safe on a couple of pieces of furring strip for a while. I know that messes up the idea of anchoring it down. but I wouldn't want the bottom of the safe wet, either.
A moisture barrier between the safe and the concrete might be worthwhile, if you could get the safe in place without tearing the barrier.
Myron
