Do you think it would be a bad idea to talk about this hobby during an interview (if appropriate) or would it come off as weird?
I think you can talk about virtually anything as long as you do it cautiously, cognizant of how it might come off as to your interviewer.
"Got any hobbies?"
*Names some less controversial ones, then:*
"I've also gathered this recent fascination with watches: their quality, how they're made, their history, and so-on. Unfortunately, quality comes at a pretty price-tag—and I'm definitely not in a position now to go beyond internet searches!" *Throws in some light laughter.* "I got really lucky when X relative, knowing that I had this newfound interest, offered a nice watch of my choice as a graduation gift. I was very thankful and excitedly accepted the offer, and I've really enjoyed unpacking all there is to know about it."
I came up with that in 1 minute. It's not perfect obviously, but with practice and some thought, I'm sure you can come up with something that isn't "off-putting."
A lot of the times we ask for other's opinions on what to say during interviews, but really, above all, I think one needs to be honest.
Just tell them what your hobbies are! That is when passion shines through, when they can tell you're not a 4.0/525 robot with no personality. I've found that when I overthink, that's when I flounder and feel awkward. What I'm about to say is extremely cheesy and cliché but it's true: if you "speak from your heart," I don't doubt you'll leave a good impression.
Don't think too hard. They wouldn't have sent you an II if they didn't like you. Just show them who you are.