In general about an hour, depends on the guide and if the group asks alot of questions. But no more than an hour and a half.
Between an hour and hour and a half. It was was a wonderful tour. The Opera House is BEAUTIFUL!
Although the tour is 1 hr 30 min, you are free to stay as long as you want, revisiting everything you saw.
Ours was 90 minutes. The group had several questions.