I will say that I never played this piece through beyond reading here and there.However ... a good friend of mine prepared it for a competition last year and I got to hear all my teacher's comments on his playing, so here's my take:For the purpose of screwing around, the first movement of Tchaikovsky is quite fun, and there are many quasi-virtuosic passages that are not that hard to fake or even pull off moderately well. The real challenge comes when you try to tie the whole thing together--memorizing it, preparing it with an accompanist, playing it over and over again to get it ready for a performance. That's when it becomes impossibly hard. The piece is absolutely huge, and one has to maintain the huge breadth of phrasing throughout, maintaining steady tempos, and very clear articulation, not to mention playing the technical passages absolutely effortlessly. This concerto is a warhorse--it is extremely well-known, and to be taken it seriously you must play it in a fast tempo with all the energy that Tchaikovsky demands, which includes pounding out the treacherous octave passages with the force to match an entire orchestra (while somehow maintaining a brilliant tone and intelligent voicing). I would recommend playing (or at least checking out) Liszt's Eroica Etude to get a feel for how it's going to be--the length of that octave passage in the Etude is not dissimilar from those in the Tchaikovsky. I will add, as a caveat, that the third movement is even more difficult and technical, and there are fewer places to hide.I would estimate a year for myself to prepare this to a high concert level, based on my skill level and experience as a first-year master's student (for context: I have played four Chopin Etudes and am working on three more right now). For you, it would probably take 2-3 years of slow, section-by-section practice, in which you have no true idea of the scope of the piece, and it only begins to take shape in your mind after many, many hours and run-throughs.