When using manuka honey in sinus rinses for chronic or recurrent sinusitis, for how long do you recommend treating?

I Wouldn't. I wouldn't recommend using manuka honey. I do recommend the use of saline rinses and neti pots (with saline), but the studies with manuka honey are limited and primarily lab based. There are too many things that could go wrong with use in your sinuses (contamination, purity, ineffectiveness, etc.).