I would first ask what you really want to "do" with the language, and how proficient you want to be.
If you perceive a language merely as a communicative tool or a vehicle to absorb information produced in a different language (reading, watching tv, listening to radio) I would suggest not to bother too much with 'advanced grammar'. You obviously still need to grasp some of the basics otherwise you'll never be able to convey meaning. (syntax, semantics, etc.)
If you want to immerse yourself in another culture and use a language almost anthropologically, ie to uncover the meaning of other peoples lives, cultures, societies, systems of meaning, a much deeper level of language comprehension is required.
I have always found that studying grammar gave me the best results, not always the fastest, but the most durable. This might have something to do with me studying Latin in high school for ~5 yrs, which is very grammar heavy. Perhaps it was formative for my ability to learn languages, although speaking a dialect helped too.
3 reasons
- You'll master the backbone of the language. Once you know grammar, you can basically apply the general rules in every situation, while using different words. Grammar is like a Christmas tree. Once the tree is up, you can start decorating the branches.
Immersion then, I have found, adds a lot of vocabulary and increases your processing speed, so you'll be able to express yourself better (more detailed, specific, more nuanced) and faster. Full immersion also gives the quickest results, but it's not an option for a lot of people.
- If you know the general rules, it's much more difficult to lose the ability to use the language if you have not been able to keep it up. Once you open your grammar book again, you'll quickly pick up the basic rules, and you'll easily retrieve the words that vanished from memory.
- It'll greatly increase your ability to actually write the language. Learning by ear only is great for casual situations, buying a loaf of bread etc, but once you start writing, you have no clue how it's actually spelled. A language is active (writing, speaking) and passive (reading, listening). Without a good study of grammar, it's difficult to be proficient at the active level.
In any case, learning a new language and become fully proficient, is always difficult and often painstakingly slow. So be prepared to put in the time; the more the better. If you only have 2-3 hrs per week, I am afraid you won't get very far. I'd recommend at least 6 hrs of actual study, excluding passive consumption (TV, radio).