Is it possible to over-prepare for a meeting?

Good question, and it's tricky as this isn't exactly math/science. If I were to put a number on it, I think a good max is mirroring the meeting length. So if you're prepping for a 45 minute technical review meeting, spending >45 minutes seems like overall.

Something I want to call out is that meeting preparation doesn't have to be only before the meeting, it can be after as well. After any substantial meeting, I recommend reflecting on how it went (read the meeting notes if those exist) and what the most salient points were. Try to extract patterns from what the more senior engineers are saying and try to say bring up points among similar lines for future meetings. You'll find that certain meetings have certain cadences, and once you understand them, you can plug in and contribute more.

Is the concern around how over-preparation might be perceived in a meeting? (i.e. "you're trying too hard") I've never experienced that, so in general, more prep is better!

However, the opportunity cost is real, if you decide there are better ways to spend your time.