How many hours should I practice flute?
How much time you set aside is really up to your schedule, but anything between 1-4 hours a day is good. However, quality of practice is far more important than quantity, so if you only practice for 30 minutes but in a detailed, mindful way you will get a lot of benefit from that.
How do you practice flute efficiently?
ALWAYS practise at the very least sitting straight in a chair with both feet on the floor. Even better, standing up! Bring the flute to your lips, don't slouch forward to reach down to your flute. Have a proper music stand and your music set up at about shoulder height.