Some time ago, a course I visited had final exams, and the time announced to the students in advance (several weeks earlier via email by the instructor) was 3 hours. Rather shortly after the students began to write (about 20 minutes), it was announced as a clarification that the room was booked for 3 hours, while the test itself would only take 2 hours.
I did not take part in this exam (I took the second one, which had similar conditions), but I'm sure the students were quite surprised. The exam itself was of average difficulty, had it been 3 hours, but very tough in only 2. This was reflected in the results: 90% failed, instead of the usual 30-50%, and the best grade was only a "B-".
I'm interested if this sort of thing is less unusual than I would think, or if there is a protocol how to deal with it as a student?