Well, anything that violates the flow of time would be a breach. Simply (ha!) casting a spell to travel forward, or back would violate it. Like violating it to save a loved one, or stop a tragic accident. Or even, just enough research to know how to start the ritual (because a ritual it would have to be) when *somebody* stepped in and stopped them. Heck, divining the future with any accuracy could be a violation.
Though my personal favorite in that line of thought, is a character that *has* traveled back in time, stopped a horrible tragedy from occurring. Only to have made things even worse. And then for fear of causing further harm to the "timestream", has not set thing back the way they were. Which would mean he has a potental for knowing future events, but definitely not accurate in those "predictions".