yes.
depending on paint, application, humidity, thickness, number of layers, temperature and so on, it could take anything from a few days to a couple of weeks to air harden.
We have some prototypes at work at the moment that have to be put into a full, padded, body sock to protect the painted panels while the car is being built, as due to a couple of the features (that won't be there for production!!) the body shell can't go through any sort of heating process to cure the paint. So a standard car takes 12-18 hours to harden sufficiently for the production line (another ~100 to reach full hardness IIRC) and the protos have to be shipped in an enclosed truck to protect the still slightly soft paint (about 3 weeks to go off completely). It is about 25 coats in total though, instead of 8-10.