What's the recommended temperature for chocolate to set?
The recommended temperature is 20°C. This is 12 to 13 degrees Celsius difference to the actual chocolate temperature. 1-2 degrees deviation will not be a problem, but more than that and you will get subpar results. 

This temperature should ideally be the same on all sides of the new chocolate shape. This means, if you are covering something in chocolate, you also have to balance the temperature of the surrounding air, the covered thing ("core"), and the chocolate. In this case, you also ideally have 20° covered thing, 20° air and 33° chocolate. But if you really have a deviation, you should try to at least have air and core at the same temperature, so 22-33-22 is better than 18-33-22. 

I also once wrote an answer which adds detail from an article on tempering truffle couverture, you can find it at this question.