How can I cool chocolate in a couple of minutes?
The short answer is: you can't. 

The long answer: chocolate has very complicated thermodynamics. There is an optimal speed of the cooling process, and it is slow. Chocolate should be tempered to 33 Celsius (there is some variance depending on the cocoa content) and cooled in an environment between 27 and 20 Celsius. Then it looks and tastes good. 

Chocolate which has been cooled in a cold environment will not have any shine, and the colder you get, the larger your problems will be. You can even get uneven distribution of the cocoa fat, with it pooling along the nuts on the inside and letting the outer layers unpleasantly dry. Besides, you will get condensation, which is ugly and makes the chocolate sticky to handle and watered down in the mouthfeel. In extreme cases, you may even end up with distempered chocolate, especially if you don't have seed crystals. 

No matter what you are doing - truffles, chocolate dipped fruit, pure pieces of chocolate in a mould - you can't rush it and get good quality.