Congrats on working out the piece you want to play Radek!
Figure out something just now so hope it could help a bit =]
I think to be able to play the whole piece in one go takes slightly different approach, such that it is okay to make some mistakes, but to make sure the entire song flow is good enough. The goal is to play till the end, so endurance matters more than precision. It would then takes months of playing the same song to get the smooth playing you want.
Experiences would then reduce the amount of time needed from zero to mastering, a great example would be Sungha Jung 
Happy learning!