It's pretty much impossible to answer your question. If your humidor is located in a room where the relative humidity is never lower than 60% and never higher than 65% the answer to your question is "never." If your humidor is located in a room where the relative humidity is 10% then you probably should "dip" it about every other day.

You should have a hygrometer in your humidor that tells you what the humidity is in your humidor.