There are tons of ways to nurse, no right and wrong way, so don't take this personally, you do what works best for you & YOUR baby, but here is how I do it and why, it's worked perfect for me!
Since the beginning, I offer one breast each time I feed only, because the milk you express at the beginning of a session has thinner consistency, relatively high volume and low fat.
Then, by the end of a breastfeeding session, the high-fat hind milk is thicker, richer and creamier, which is great for baby!
So focusing on one breast each session ensures that they stay long enough to reach that high fatty milk, not just the fore milk.
I do this since the beginning of nursing, so my body adapts to it quicker and I don't need to pump or express the other breast, it regulates to one each time, and as often as I demand it.
As for TIME, I let him lead. Sometimes he wants to nurse for 10min, sometimes 30min, he is the boss, he knows how hungry he is and what he needs!
Slowly, as he grows, he will eat less often, and more quantities. But my goal is to always feed him more frequently during the day, so he does not need as much as night and we can sleep some longer stretches and hopefully, through the night eventually.
But remember, every kid is different, I also nursed like this with Sofia (one side and tried to offer more during the day) and she still woke every 2h at night during over 6 months...
I always feed on demand, but the first few weeks, to ensure baby weight gain, I do wake him up often (if he does not ask for it before). Click here to read my "schedule" for the first few weeks to ensure the weight gain!