Your mentor doesn’t need to be there every time you teach. How much support you feel you need is at the discretion of you and your mentor.
If you are teaching someone or running a practice for the first time, you might well appreciate your mentor being in the tower with you quite a lot to begin with, or you might be quite confident and happy with just the occasional visit.
Your mentor will need to look through your log book and be prepared to witness the different aspects of your teaching required for accreditation. When you both feel happy with your level of teaching, they can ask an ART Assessor to come and observe you teaching and then submit a recommendation for your accreditation.