If the muzzleloader has been kept at the same temperature and you didn't sit in a rain storm, then I would leave it until the next morning or a day or two. My concern isn't so much about the moisture and fouling, it's the corrosion of having a dirty barrel sitting around for awhile. It's not a problem, if you don't foul your barrel prior to loading for the morning, but your accuracy will suffer if you don't have a dirty barrel. I've learned my lesson from not doing so and missing at relatively short range. Good luck.
From those who much is given, much is expected