Pausing from where he was pretending to browse, Theo turned to look at Hermione. He couldn't fathom why anyone would want to chance going back, not to mention the ramifications of that action. It was a curious thought.
"Well," he said leaning with his back against the stacks, "You can't change time. Not really. Not that I've heard," he said thoughtfully. "You can try. But things meant to be will just inevitably happen, just at a later date. Time has rules. Moving ahead is one thing, but back. That's a whole other situation. What is meant to be has already passed. Best to work on what we have now, and maintaining it. Or at the least safe guarding it," he said with a slight smile. "Wouldn't you say so?"