How to preserve cotton candy
It seems the best thing to do is to have a sealed container with little air in it.
CO2 has proven to be useful, but its presence is not as important as sealing.

So, if you want to preserve cotton candy, my experimental results show that a sealed container is preferred. I obtained a conservation of 24 hours, but probably it will least 48h or even more.

EDIT: Well, sealing seems to work pretty well, but I have to report a pair of failure...
2 out 5 packages did not preserve the cotton candy for more than 24 hours, while the remaining did. On the plus side, the first experimental sealed package preserved cotton candy for more than a week.