> 10 minutes a day, whether duolingo or not, will get you further then 70 minutes once a week in a crunch mode. That holds for language, playing musical instrument, sport, whatever. The hardest part in those is to keep interest and touch with activity over the long time it requires. And the big enemy are months when you pause the activity entirely.
My point is that you need both. Reviewing vocab etc. can be done as part of the "daily 10 minutes" (although it usually takes me longer). But learning about new grammar etc. usually takes longer than just 10 minutes. And once in a while you just have to sit down and read a more complicated text, looking up vocab, etc.
Again, it pretty much also depends on the language. For Japanese, I think it's impossible to get anywhere with just 10 minutes a day, I think.
10 minutes a day, whether duolingo or not, will get you further then 70 minutes once a week in a crunch mode. That holds for language, playing musical instrument, sport, whatever. The hardest part in those is to keep interest and touch with activity over the long time it requires. And the big enemy are months when you pause the activity entirely.
Obviously you have to mix the learning modes. And obviously the more time you put into it the better.
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I also think that people get naive about amount of time people actually spend learning when going to classes in school or after school club. Typically, get 1-2 lessons a week plus some homework. Sometimes you get 3, but any more then that is unusually intensive. The typical expectation when going to in-person classes is that yes, it will take years till you are anywhere near good command of the language. That a year after, you can survive your way, but still cant consume most of normal media without subtitles. Those are reasonable expectations.