If you want to respond in the evening, you can say "buenas noches" (good evenings) or simply "buena noche", as you mentioned. In more informal settings, you could also use a casual greeting like "noche buena". If your tutor is comfortable with it, they might appreciate a slightly more formal phrase like "a buena noche". Regardless of which one you choose, remember to practice your pronunciation so that it sounds natural and smooth.