It took me about that amount of time of actual study to be able to "lex" spoken Cantonese into phonemes. It's a weird experience that happened nearly overnight -- it went from "incomprehensible wall of sound" to "stream of sounds, with clear start/stops" very quickly.

IIRC the early language acquisition literature supports the idea that exposing a child to the sounds of a language (even without any actual instruction or even requiring the child to pay particular attention to the person speaking) is enough to make it much easier for them to understand and produce that language later in life.