We know that bad things have happened to wizards who traveled through time. Some have ended up killing their past or future selves, we were told.

How many times did Hermione say that she and Harry "couldn't be seen" by anyone when they traveled to the past to save Sirus and Buckbeak in Prisoner of Azkaban? Before she and Harry traveled back, Dumbledore reiterated the point: "You know the rules, Ms. Granger. You must not be seen."

It hadn't occurred to me until I listened to the audio book for the nth time that Hermione not only did the very thing people traveling through time are warned against, she did so with the Ministry of Magic's blessing! Hermione appealed to Professor McGonagall for a Time Turner so she could increase her course load, and McGonagall managed to convince the Ministry that Hermione would use it responsibly. So with the TT, she'd attend a 9 a.m. class, and then travel back in time to attend another 9 a.m. class.

Hermione was seen. Didn't that violate some kind of rule? Obviously, the Ministry and McGonagall (and Dumbledore) thought it was OK. If that's the case, why the repeated warnings when rescuing Sirius and Buckbeak? Was it because there were two of them?

Color me confused. Perhaps I missed something in the book.