The Russian course is nearing completion!
According to this page - https://www.duolingo.com/course/en/ru/all - the Russian course is about to exit the beta. To be precise, it's 95% completed. It looks like it will be the first incubator course to graduate from beta. However it is followed closely by the Dutch course, which is at 92%.
It looks like from start to finish it takes about three months, at least for a faster type of course.