How long can the swelling caused by bursitis of the knee normally take to go down?

Knee bursitis. This depends on the cause and the severity of the bursitis. If the cause can be haulted then swelling can start to decrease slowly over weeks to months. If the activity causing the bursitis is continued then the swelling may be persistant.
Varies. Depends on the severity of the condition and if the underlying cause (such as repetitive trauma to the area) has been eliminated.