Final answer:
The first stars were created around September 10 on the cosmic calendar, which compresses the time since the Big Bang into one year.
Step-by-step explanation:
According to the concept of the cosmic calendar, which compresses the time since the Big Bang into one year, the first stars were created around September 10. This is represented as the evening of December 31 on the cosmic calendar. It is estimated that these stars formed around 400 to 500 million years after the Big Bang, as the universe continued to expand and cool off.