I've got the reputation of being a workaholic. It's been said that I'd spend ten or twelve hours a day at the piano and that after each of my concerts I'd lock myself away for nights on end in order to continue working on the pieces I'd just played. Nothing could be further from the truth. If Iworked after a concert, it was to rehearse or to put the finishing touches to new works for the following day's concert. Also, with my German pedantry, I decided ages ago that three hours a day at the piano would be my normal ration and that I'd stick to it as far as I could." Let's work it out. 365 times 3 is 1,095. That makes 1,095 hours a year that I need. Days spent travelling by car without touching a piano, concerts demanding several hours of rehearsals (which I don't count as instrumental practice), bouts of illness or indisposition and periods of interruption which, on occasion, have lasted up to five months at a time - they all have to be made up for. I keep a stopwatch on the piano and try to keep an honest record of the time I actually spend working, but I admit that there have been times when I've had to work a lot more, especially on the final day - for example, when I had to learn Prokofiev's Seventh Sonata in four days or Rachmaninov's Second Piano Concerto (not such an easy work!) in a week. But, in general, no. ...I adopt a purely repetitive method whenever I've got to learn a new piece; I identify all the really fiddly bits and study them first, practising them mechanically. I take a page at a time, go over it as often as I need to and don't move on to the next until the first one is under my belt. And only when I've finished the second one do I move on to the third. However difficult it may be, there isn't a passage that doesn't become easy if practised a hundred times.
Sometimes you just have to put in the hours...
Richter on Practicing