what kind of refrigeration are you using - a home fridge? industrial walk in cooler? industrial reach in? the level of humidity will be different in each type.
Are you making your own fondant or using a commercial brand? Most commercial fondants say they don’t succumb to condensation, but this is not true.
I have a very humid walk in cooler and a humid reach in. I have the “best” results when I put a fondant covered cake in a box, and then wrap the box in a large sheet pan bag. If I don’t do this (and there have been times when I haven’t) then the fondant will weep as it comes to rm temp, and if you were painting on the fondant, the painting would be ruined.
So, if I were facing 36 hours of work, I’d test it first.
I’m just curious: What are you using to mix the luster dust with? Are you using a US brand or a European brand of dust? I have a few jars of dust from Squires Kitchen and find the color very deep and beautiful. Not that it is better than the stuff we can get here, but just different.