The key to success is daily practice. The more you practice, the more progress you can expect. It is difficult to set an exact amount of time, but it should be everyday and as much as possible.
For wind instruments, part of the development process is a strengthening of facial and abdominal muscles. As strength and stamina increase, so will the length of practice sessions. Also, as the student advances, a wider variety of lesson materials will necessitate greater practice time.
The bottom line of any practice session is improvement. If an hour is spent, but nothing is improved, then you have played a lot, but not practiced. On the other hand, if improvement is realized in 15 minutes, you have practiced. Hopefully, at this point, you will be encouraged and will continue practicing to improve even more.