Experience, Time and profiency

I don't think those numbers exist, it's so individual to the person learning what they can and can't conquer. I think consistency is key above all else, find a rhythm that works for you, and stick with that, and you should see good results.

To give some sense of direction here, I'm going to reference the things I've read on this topic. I've gotten two conflicting answers here, honestly.

One source (a programming bootcamp) says it's important to spend large chunks of time working on programming. An hour here and there doesn't make the cut and allow for "optimal" learning. My opinion is that if you've got an hour, it's better than nothing. They also cite about 15-20 hours a week (3-4 hours a day, 5 days a week) as the ideal minimum to spend on it to make progress. 10 hours, they say, will significantly slow your progress... but you will make progress.

Other sources stress the need for habit. The #100DaysOfCode challenge is all about spending an hour on code every single day. If you code in a big chunk one day but don't touch it for another week. you won't progress as quickly (but again, you will progress, even if you're making it harder for yourself).

I think it's important that you take this information for yourself and find out what works for you. A good starting point might be 10 hours a week: 2 hours a day 5 days a week. For you, that starting point might be 5 hours a week, or 20. What's good for you really depends on your situation, so you have to think about where you're at and what your goals are. If you want to get a developer job as soon as possible, then obviously the more time you commit to studying, the better.

Don't forget, though, that the way you study is also very important. You must work deliberately and not passively. Don't just watch the videos and do the minimum that the code examples ask of you. Play around with things. Take notes when you learn something new. And most importantly, build things. If you're learning code and programming languages, take the things that you learn and apply them to some assignment or project. For example, I'm studying HTML. It's basic for me because I've studied it so many times, but I never sat down and immediately applied things, and HTML5 is relatively new, so even while doing a relatively boring review, I'm still learning new things or finding topics that I need to apply hands-on in the way I structure a page.

As for the "max" you should be proficient in, I don't know. Specialization is valuable and it's helpful if the things you learn relate to one another, as that makes learning each thing easier. I'm studying web development, so learning HTML, CSS, JavaScript, PHP, Wordpress, and an additional backend language or two might all be useful in advancing my career. But I also want to study iOS development for fun, because I got an iPad and I want to make it do my bidding. Determine your goals, and that will help you find your answers. If you don't understand why you're taking a course, you might be better off taking a different one or establishing some reasons and motivations.