Learning Period

Question

I see so many varied answers as to the question “How long per day should I learn X”, some say 30 mins, some say an hour others say learn as long as you want and while the first two promote consistency and growth, I feel that 30 minutes a day is good enough for learning anything, of course, the more you invest, the more you can take out, but I feel like there is infact a widely accepted period of time for learning anything, I think 30 minutes is always more than ample, but what about you??