This is a question I get a lot from learners on renshuu, and so I'm writing down my thoughts on it so you can hopefully benefit from it. This answer is based on my years as a language learner and as a language teacher. Long answer, but I hope it helps.
1. First, comparing yourself to other learners is almost always a bad idea, both in terms of study time as well as progress. We all lead different lives, and that leads to both different amounts of time that we can study, as well as differences in study time "quality". By this, I mean that someone who is well rested and living with low amounts of stress will typically get more out of 1 hour of studying than someone who is lacking in sleep, and/or experiencing higher levels of stress because of other things in life.
2. For most of you, your goal is to achieve a relatively high level of Japanese comprehension so you can read, write, communicate, or do what it is you want to do with Japanese. This requires you to reach that goal, naturally. So if you want to be able to read Japanese manga fluently, and you only learn half of the words commonly found in manga, then it doesn't matter how hard or how much you studied, you aren't going to be able to comfortably do what you wanted to do.
So, reaching your goal (or put another way, not giving up) is overwhelming more important than how quickly you reach it.
How does this translate to real world actions? I strongly believe that for most people, studying is something that should be done in short enough chunks that you should not have to think and argue with yourself as to whether or not you're going to study on any given day.
For most people, an hour of daily studying is quite a lot, and depending on what else you have going on for that day, you're going to need to decide each day whether or not you're going to put in that hour of studying. Since a decision is involved, there are so many influencing factors that could lead you to say no: busy day, feeling down, sleepy, etc. So you may study an hour each day, but only 2-3 days a week. And of course, we are all familiar with the feeling that the longer you don't do something that you're *supposed* to do, the harder it is to get back into it.
I believe that initially, your study amount should be low enough that you don't even need to make a choice to do it each day. "10 minutes? Of course I have ten minutes to study, why wouldn't I?" - this is the kind of interaction you want to go on in your head, not an "Uh...do I feel like studying today?". Studying should become habitual, because learning a new language simply isn't something that the overwhelming majority of us can sprint through. It has or will take years for many of us.
Naturally, even with small amounts, there will be days that you simply cannot study, and that's ok. At renshuu, we don't rely on negative reinforcements. But you really want to set yourself up for daily success, not a daily challenge of forcing yourself through something uncomfortable.
Start low, maybe even comically low from your perspective. Get 10 minutes done a day, make it so easy that it's a daily win for you, and then you can slowly start to increase the time if you feel like that is best for you.
Again, this is not an objectively ideal way of studying for everyone. It is one, though, that I believe will help many learners, especially ones who have tried other learning challenges in the past, but found themselves burnt out all too soon.
