Even though we can trace our cosmic history all the way back to the earliest stages of the hot Big Bang, that isn’t enough to answer the question of how (or if) time began. Going even earlier, to the end-stages of cosmic inflation, we can learn how the Big Bang was set up and began, but we have no observable information about what occurred prior to that. The final fraction-of-a-second of inflation is where our knowledge ends.
https://medium.com/starts-with-a-bang/did-time-have-a-beginning-5bbb690df291
https://medium.com/starts-with-a-bang/did-time-have-a-beginning-5bbb690df291