People often ask me how many hours one must spend outside of class per hour inside of class to succeed in a university-level math course. I hesitate to answer. The reason is that the question is ill-posed. To really understand the logical structure of mathematical ideas, how they work and fit together, why they exist and work the way they do, one must really spend the time to dig into every nuance of the idea. To do this on a research level, a mathematician understands that she must isolate herself from outside distractions for sufficient periods of time to fully explore the structure of a new idea. The isolation-booth manner is as vital to the process as deep, dreamless sleep is to the health of a person. I call the process of getting to the level where one can focus exclusively on the task at hand without distraction as "going deep". It is kind of a meditation-type thing, and only really works when one practices it regularly. It can be dangerous, though, as the day-to-day tasks tend to get neglected. But it is quality time for understanding complicated mathematics, and easily outdoes simple quantity time when the latter is filled with noise and attention-taking "shiny objects" (distractions).
It's loads more productive to spend an hour in an isolation booth environment focusing solely on your mathematics work instead of 3, 4, or 6+ hours poring over books and notes while checking your phone, listening to music or chatting with friends (or potential friends). Distractions keep you from "going deep" and really digging into the conceptual and logical structure of the math you are doing. And if you do not allow yourself to go deep to really get a concept or idea, you wind up simply memorizing facts and patterns. While this may work for problems just like the ones you have seen, the minute a problem of a different form comes up, you will be lost.
Hence, there are no good guidelines in the form of "6 hours of study per hour in lecture". Studying is a personal thing, and the studying environment matters. If you refuse to allow yourself NOT to fully understand a new concept, then any and all time spent in the pursuit of full understanding is worth the effort. To do it right, allow yourself the ability to "go deep". Then you minimize the time spent to only the quality time.
Some people brag about their ability to multi-task. To me, the ability to mono-task is the lost art in society.