Where would you time travel to? (Please read the setup)

I’d go back and hear one of Rossini’s operas, in his own lifetime. Just to witness the vocal techniques used at the time, e.g. vibrato.

I’ll gather the pitchforks, the rest of y’all get the torches…

As nice as it would be to see the Burgess biota, they are mostly variations in phyla we know and are familiar with today (even if different in details.) If I had only one visit to early metazoan life, I’d have to visit the Ediacaran biota and see if I could figure out what the heck some of those things are within the “look but don’t touch” limitations set up by the OP.

I’d go see Shakespeare do an original play at the Globe. Maybe Romeo and Juliet.

That’s given me a better idea - go see Farinelli and Senesino performing Arteserse in London. Not only would we finally get a decent recording of what good castrati sound like but the performance was notorious for Farinelli’s technical brilliance. I can think of a few musicologists who would sell their firstborn for a recording of that.

Well, Jacob’s Ladder was a dream, so what you’d see of that one would just be a dude sleeping.

If I’m going back I’m going whole hog. Send me back to the first Indus valley settlement with over 10,000 residents.

Yes yes, the Indus civilization would be very cool to check out.

Which future?

Yeah but as far as we know, most of the Ediacarans would just be … sitting there. I want to see Anomalocaris do its thing. Note that by the terms of the OP, any truly groundbreaking insights will already have been done by other people.