Hey user, you’ve been selected to join a special operation. We wish for you to test out our brand new Time Machine! This is a very early beta stage, which you’re allowed to be in any point of history at any time. However you can only get five minutes of recording footage. You’re unable to alter anything in the area, nor can you change the chart of history. Everything will go on as it is, whilst you just watch and record at your discretion. All ill effects have no effect on you, you’re completely immortal and just a ghost. No one can see you, no one can touch you, and no one can perceive you. Where do you decide to go?
It feels like a bit of a cop-out/easy answer but I have to go with dinosaur times, preferably late Cretaceous. I just want to see them in HD 3D!
I'd go back to the beginning of the universe just to see how it really happened and what it looked like, lol.
I'd likely use it to go witness the Christmas Truce of WW1. It was one of the last times that truces, especially on a holiday, were honored and this event got censored badly so all we got to go on are a few diaries and second or third hand accounts. Even with all of that aside, seeing enemies stop fighting and playing games, giving gifts, and sharing drinks would be amazing to witness firsthand.