"I lived and studied under the path (where the banking occurs) of the Rwy 13 Approach back then, it was noisy enough to interrupt our teacher every 3 minutes for say 20 seconds. And there was "always" a plane departing in between the 3 minutes interval, although not as noisy as it flew over towards the sea. I also noticed that, the local players, namely Cathay Pacific, usually made the approach path a bit wider and a bit more towards the hill so they can have a longer final and a shallower angle of turn, then the published procedure. Also rememered I can occasionally feel and hear the wake turbulance even from a meduim weight aircraft, from my school playing ground in the good old days...Long live Kai Tak."
Accessed March 15, 2010, http://www.liveatc.net/forums/listener-forum/kai-tak-old-hong-kong-airport/5/?wap2.
Based on the above account,
In a typical elementary school day of 6 hours (360 minutes), the teacher stopped a total of 40 minutes.
In one school week of 5 days, the teacher stopped a total of 200 minutes or 3.33 hours.
In one month of 21 school days (assuming no public holidays), the teacher stopped for a total of 70 hours.