Yoga is a great way to combine sports, relaxing and improving your happiness!
Mostly, I practise while watching yoga video's on Youtube. That's easier than trying to practise while you're bungling with a book to find out which excersises you have to do. As far as the duration is concerned you can choose whatever you like. When I practise, I choose for 45 minutes, but you can also choose for a shorter duration. You can even choose your level!
I'll post some examples underneath.
Namasté and good luck!