It is important to have a correct approach to practice. You will benefit more from several short practices (e.g., 15-30 minutes per day) than one or two long sessions per week. This is especially so in the early stages, because of the basic nature of the material being studied and also because your lips and facial muscles are still developing.
In a practice session you should divide your time evenly between the study of new material and the revision of past work. It is a common mistake for semi-advanced students to practice only the pieces they can already play well. Although this is more enjoyable, it is not a very satisfactory method of practice. You should also try to correct mistakes and experiment with new ideas.