How much time until mom enters final stage of Alzheimer's?

My mother finally got a diagnosis of advanced Alzheimers. She still knows her loved ones, and I believe she is still hygienic. However, she is hallucinating all the time, wanders, has sundowning, and gets aggressive occasionally. She still remembers trips we took years ago, but not what day of the week it is. She deteriorated quite a bit since December. I just don't know what to expect...how much time does she have til she enters the final stage and then how long until death? It seems to vary so widely.