Great question. As we begin our Buddhist practice, chanting even for 15 minutes feels like a long time and is deeply satisfying. While if we have been at it for a bit, we want to chant longer and go deeper.
So how much should I chant each day? The important question to ask yourself after chanting is, How do I feel?
Illustrating this point, the Buddhist teacher Daisaku Ikeda breaks it down:
The main thing is that you feel deep satisfaction after chanting. There are no hard-and-fast rules about having to chant a certain number of hours. ... Most important is that our chanting be satisfying and refreshing, so that we can exclaim when we’ve finished, “Ah, that felt good!” By reinforcing that feeling day after day, our lives naturally move in the most positive direction.
Of course, there are crucial moments in life when we are facing a huge problem or challenging a troubled relationship and feel that we want to chant more. That’s great. How much to chant is completely up to you; feel free to do what you think feels right.