If the temperature in your kitchen is 70 F or below and the humidity level in the kitchen is less than 50 percent you can leave the chocolate out after making it to allow it to set.
But if the temperature in the kitchen is above 70 F and the humidity is 50 percent or above then for best results you should put the chocolate in the fridge for it to set.
However I've always just placed the chocolate I'm making in the fridge to allow it to set properly.
The chocolate should set in the fridge within 15 to 20 minutes however the thicker the chocolate layer the longer it will take to set.
But most chocolate should set in the fridge within 30 minutes at most and when you're ready to serve the chocolate just allow it to sit out at room temperature for 10 to 20 minutes.