So there is a number...

1000
"+" Ofcourse it can't really be quantified - 1000 is just a rough 6 months x 6 hours per day. For that to be enough demands a well thought out approach, and lack of any significant technical challenges (as in you understand how to and can successfully solve technical challenges without excessive experimentation or help from a teacher) also I think.
Considering approach, if you were able to play through fluently at half speed with the prok 3, you'd be looking at 6 full repetitions a day on that schedule.. which is not only very few repetitions, it would also be a mental marathon that requires a whole other level of preparation in itself. The ability to learn/process/memorise lots of complex information quickly needs to be there..
You need to be able to find and internalise good movements and coordinate sections up to speed quickly, if you have to play slowly you're in trouble right? or at least its going to take you a very very long time to learn the work.
You can do 10 slow repetitions of an smaller but very difficult etude, it'll take you an hour or so. 10 slow repetitions of a concerto could take in excess of a whole day. Not that you'd do that, you'd do a smaller section.. but then you've got so many sections to deal with.. the time frame is still similar.