Hi-Lo takes about 20 seconds to "learn". It could hardly be simpler. Learning to use this to give yourself a decent edge at a casino table is a totally different thing however, and takes probably around 100hrs+(not an accurate figure I'm sure) to grasp well enough to use. Then there are further things to learn like indices etc.
It all depends, as QFIT stated, on what your definition of "learn" is, and what it is you are claiming to learn (or what a company claims to teach); the principle of a system, or the full system in its entirety that can be used to beat a casino.