Theo hadn't thought of it in quite those terms before, but it resonated deeply. "I think I do know. At the same time, I don't actually want to spend all my time here locked up in my library avoiding people. I did enough of that back home, so...I guess I'm just going to try to be braver here than I was there. There aren't any guarantees about our time here, or what we'll remember when we go home, so it's a matter of determining what's important." He wasn't sure if he was making sense, and he didn't necessarily disagree with what Percy was saying, so much as he'd decided to experience life here and trying not to worry about what-ifs. Which was all easier said than done, honestly.
"It's a possibility if you're not careful or rush the process. I am both careful and patient, and transfiguration is one of my best subjects, so I don't think I need be too concerned about it." Hopefully, he was right and there would be someone who could help put him to rights if he went wrong, but if thirteen-year-old school children could accomplish it, he thought he had a good chance. "Oh. It's actually a month. I misspoke earlier, and it's actually full moon to full moon. So...twice as difficult probably."
He grinned at the other man. "Wonderful. You can take that copy with you if you like. It's not a first edition or anything, so you're welcome to keep it," he said, gesturing to Hogwarts, A History. "You're welcome to borrow any of the others, as well. Those I would like back though." He supposed that wasn't necessary, that his books would reappear at home when he was sent back, but he didn't want to change anything. "They're used for medicine too, along with various other things. They're the only known cure for someone petrified by a basilisk, for example. And, of course, the animagus potion. Horrid creatures, but useful."