Steve F. answered 06/06/19
Writing Coach and Award-Winning Editor
The sentence examples you used are a bit redundant. Also, the definition of singular doesn't mean that history cannot be filled with millions of singular moments, things and events.
You could simplify and still convey your intent with sentences like one of these: History began with the first recorded moment. The moment when time began will forever be unique.
If I want to fill in the blank of one of your sentences, I would choose the following and come up with a good result that also conveys your intent: The moment time began is the __a unique__ moment in history.
There are plenty of possibilities and no limit to the fun one could have with your singularity challenge, such as substituting "single" for it. Good luck!