Two years ago I photographed a nova in Delphinius. My regret is not following up over the year to observe the fading of the nova. Therefore, I have no personal estimate of how long a nova will last. I know it's not hard to research, but I prefer to observe first, a bit like reading a book before watching the movie.
Sagittarius is a summer constellation, so I will have a good six months to observe the nova's decline.