I usually do a maintenance soak/clean once a month as part of the overall cleaning checklist for my equipment. If you are using commercial soak, just takes a few minutes to set up and then soak overnight or forget about it during the day and finish up at night. If not making cheese that often, 1-2x/year should be enough. If you're soaking in between, and rinsing, and generally taking care of the meter, it might not ever be necessary. Good preventative measure, though.