Well, it is up to how many time you have. The answer is: as much as you can! If you want the best result, the best way is to create a situation like you had when you were a baby and learning Portuguese: immersion! It is even said to be very useful when you listen to your target language when you are not really listening and doing other things. Just let it run in the background BESIDES proper listening sessions of course. Don't only use programms made for learners, though they are very good for learning, but also listen to stuff, where people use normal speed when talking.It does not matter, if you understand hardly anything or nothing at all, your brain will do its work and start making conections in your brain. As for resources: youtube or radio stations would be my first choice or audio books. for the learning sessions: this is a good series for learners: https://www.youtube.com/watch?v=yhP3OT2hxAE If you are alright with children stories: bookbox has a good programm, the videos are on youtube as well: https://www.youtube.com/watch?v=S0uTgSBdbUg

http://www.dw.de/deutsch-lernen/podcasts-newsletter/s-11696 Das ist eine nützliche Website. Du kannst damit dein Hörverstehen weiterbringen.