Varies. It is difficult to give an "average" wait time, because the wait time is dependent on how sick the person is. At this time, there are not enough livers for the number of people needing them. A score (meld score) is commonly used to determine who is most severely ill, and most in need of an urgent transplant. One person's wait time may be much different than another's, based on how sick he/she is.
Also depends. Agree with dr. Puppala. In addition, it may also depends on the geographic location of the patient. For instance, with the same score (model for end stage liver disease score), someone get a liver early, if they are in south (such as texas).