How many minutes in a half an hour?

How many minutes in a half an hour? Chanuka candles need to burn for half an hour after nightfall. The שר התורה Harav Chaim Kanyevski שליט"א, holds that the half hour is measured in שעות זמניות of the night time. In North America in Mid December, a daytime hour* = approximately 45 minutes (Daytime = 12 X 45 minutes = 540 minutes  or 9 hours of daylight) and a nighttime hour = approximately 75 minutes. Therefore, half a nighttime hour = approx 37.5 minutes. *ע"פ הגר"א