This is a very interesting question.
I've been told, as well as read in some books, that in the very early days of Kali, the warriors would be trained anywhere from six days to six weeks to six months to become proficient with their battle skills. The whole point of such short, intensive training was to get the warriors ready for battle in the shortest time possible. The P.I.'s being the target of many foreign invasions, the warriors didn't have alot of time to develop a long, complicated combat system: it had to be learned quickly and effective - period.
These days, developing some kind of decent skill in the art of KALI depends on the individual. How much time are they willing to put in to practicing and training? Are they willing to spar (both protected/unprotected) to test their techniques under pressure? Since we (as Kali practitioners) don't have to worry about foreign invasions and such anymore, most of us train in the art mainly for our own personal interest, enjoyment, etc.
Myself, I've been practicing Kali/Eskrima since I was 14 years old (about 14 years ago) and I'm still learning! It never stops. Before I started sparring with minimum equipment, I was mainly concerned with techniques and 'looking flashy', but once I started sparring, I found my 'real' Kali skills finally came out in combat (albiet friendly combat).
Dilligent and honet practice and training will make you a good Kali man/woman, but it's also important to have a really good teacher. Your teacher will be the one to act as your guide, but it's completely up to you where and how you go on from there.
Hope this helps, and good luck with your training in this wonderful art.
Peace,
Jay