What point in time would you observe?
Imagine you could go to any one point in time, observation only. You can change nothing, you can take nothing, you can leave nothing. Nobody will notice you, it would be as if you were watching a movie. What point in time would you choose to observe? Optional second question, why do you choose that as your one point in time to observe?
In the past. No fair saying "tomorrow to see the lotto numbers".