Information Cascade example

Last week I was in a classroom that did not have a clock (I know, right.)... and this one kid in the front of class started packing up his stuff. Because no one else bothered to check their cell phones to see if class was actually over, I saw several other people behind him also start to pack up. It turned out that the one kid was leaving 20 minutes early for some reason and the other people ended up checking the time, realized class was in fact not over, and had to unpack their stuff again.
It was kind of funny.

People often look forward to the end of a class, so when somebody suggests that it might be that time, who would question it, especially if this class was longer than an hour?

If the situation were changed in that there was a clock, but it was 20 minutes fast or 20 minutes slow and the person knew the real time stayed or packed up, respectively, would others follow? Would they be more likely to pack up or check the time in one of these situations? Would someone not packing up even be able to start a information cascade or would he/she just be ignored?