Hi Sammy the hog
The normal recommended times for cleaning out hog houses is April and October. But if you are absolutely certain (i.e. have a camera aimed on it, for instance) that there is no-one in residence, you could clean it out now. Be very careful how you clear it out, just in case.
Assuming it really is completely vacated, use boiling water to kill any parasite eggs which might be in the cracks.
Make sure there is suitable fresh potential bedding nearby – medium sized leaves, grasses, etc. You can put a handful into the cleaned and dried box, to give them the idea, but they normally like to make their own nests.