If it's an every day CCW, weekly. If it's a weekly CCW, then monthly. If it sees a lot of time, relatively, in a range bag or safe without being used, then depending on your local weather (relative humidity mostly), once every 3 months is what I do.
I tend to keep the little desicant packets that come in shoe boxes and electronic equipment and so on, and just toss them into the bottom of my safe. They seem to , IMO, help out the regular safe desicant things. They certainly don't seem to hurt anything at all. So for storage weapons, I would say the 3-6 month interval will be fine, again, depending on your local weather conditions. If you are in a coastal area, I would shorten the cleaning intervals accordingly. Damp salty air is the worst thing for ferrous metals to have to contend with now that corrosive primers are all but uncommon.