Anyone ever made chocolates from a metal mold?

I have, many times.  As long as the mold is shiny and clean (on the inside of course) you should have no problems.  I did refrigerate mine (and sometimes used the freezer but more rarely).  They frost over just like the plastic molds and release easily. 

I have many old metal molds that I use (mostly at Easter time).  If you are painting them do your painting first and let it dry (drys very quickly) then paint the base color over the painted colors, this will help keep the colored chocolate from melting when you pour in the base chocolate.  Let this dry a few minutes before pouring in the base chocolate.  If the mold is a solid mold (it will be open on the bottom) tap it several times on a cutting board or hard service to get any air bubbles to come to the top then put it in the freezer.  If it is a hollow mold, once you clamp it together you want to slowly it turn it in all directions (about 5 minutes depending on size of mold), this helps to roll the chocolate evenly so you don't have thin spots.  Then you put it in the freezer.  When you are ready to unmold the chocolate you probably won't have problems with a solid piece but you may with a hollow one.  If it does not come out easy, but it back in the freezer and try again later.  It should come out fairly easily when it is set up.

A half hour should be enough.  May be shorter but I like to make sure mine are hard all the way through.  As long as there is not a really thin portion (which I haven't seen before and I have a lot of molds) you don't need to worry about it cracking.  Would love to see your finished product!