How long does teething generally last before a tooth visibly comes in?

Hard to say. Since people often attribute any unexplained fussiness to teething it is hard to decide if is even a real condition in most. Bradshaw's studies long ago showed the normal kids fuss daily but the intensity declines as they develop skills like rolling over which corresponds to the time some begin to have teeth emerge. Responding to a chilled teething ring may or may not verify teething pain.
3-6 months. Around 3 to 6 months is the average age when the first tooth begins to exit the gums . It may be accompanied by a slight fever, drooling, crying and irratability. Some babies are born with teeth and some are very slow to errupt teeth. Dont worry, unusual teething rates seldom translate into serious problems.
2months. Teething usually starts around 4 months old, and average age at first tooth eruption is 6 months old. Remember though, teething pain may recur with subsequent tooth eruptions.