So long as your practice is focused and your technique (especially left hand) is sound, you can practice as much as you want. I'd never force anyone to practice but, I'd never discourage it. If you wish to practice more than an hour a day make sure you warm up properly. Do it in half hour pieces followed by time to reflect on what you've accomplished and what you wish to accomplish. That way you'll see progression rather than sit frustrated on a line or part you haven't got yet.