My flare ups can last a few days, weeks or few months, it depends on what the trigger is. If it is an illness causing the flare up, the flare up will last throughout the illness. If I flare from too much activity, it takes a few days to get back to my norm with the help of a muscle relaxer and Voltaren gel. If food is causing a flare, a day or two and it is gone. I have found new meds can trigger a flare too. If I stop the medication, the flare up goes away. I use Voltaren gel, Ibuprofen and a muscle relaxer for mild flares and heavy steroids for severe flare ups. Hope this helps.
