How long before glucosamine & chondroitin & zyflamend start working to decrease inflammation?

They don't work. There is no data that suggests glucosamine and chondroitin have any benefit for inflammation. It is possible that they do help osteoarthritic pain. One must give it a 3 month trial before deciding if these supplements are effective.
Usually two weeks. Primary active ingredient of such combination meds is the glucosamine and that usually takes approximately 2 weeks to attain full affect. These products are not successful for all patients so if you see no response by four weeks I would stop taking it.
Depends. Some people find that their osteoarthritis of the knees feel better while taking glucosamine this usually takes between 1 to 3 months. Studies on glucosamine's benefit have been conflicting. More controlled studies need to be done to test effectiveness, safety and the best formulation.