I forget the statistic but there was someone who surveyed concert pianists practice habits over years and said something like 500 - 600 hours to reach a professional level I believe. Maybe someone has the exact stat here. Of course this is factoring in that they have the initial talent and inclination to be a pianist.
600 hours = 4 hours a day for 150 days. So it's possible to reach a professional level in just 5 months.
Rachmaninov on the other hand had to work very hard (apr 8 hours a day) and only learned a very limited repertoire despite this.
No, Rach had a gargantuan repertoire
All pianists lie about the time they practice. They all say they do less than they actually do. Thats a common known fact
He was a musical genius.When asked what the hardest piece he has ever played was, he replied 'Oh, perhaps a particular Scriabin etude, it took me a couple hours to master'