I agree, every 2 weeks or every 2 months if you do not use the bit a lot.
As Alicia said, every 3 weeks or once a month if you use the latex bit very often. If not, every 2 or 2 and a half months is ok.
Actually it depends how often you use the bit covered with latex. If you ride with it everyday, you should change it every 3 weeks. But if it is just for shows or jump, every 2 months is enough.