With an interview of this length, it is important to control pacing carefully. You anticipate what questions you will need to have covered at the 30- and 60-minute marks. Also, you plan what you will say if a student takes up too much time with digressions or repetitions.
For the open-ended questions, an important consideration is eliciting in-depth answers from the students. If needed, you plan to give each student plenty of time to think following each question (i.e., an interval of silence). Also, you think through how you will use general probes indicated in the interview protocol if you need to clarify answers or get more depth. You also decide you will get more genuine responses if you communicate encouragement along with neutrality. You plan to keep your own comments to a minimum and communicate interest through eye contact and staying very alert to what the student says.