According to mainstream Christianity when did time begin?

I’m not asking what this question asks. The statement often is made that God exists outside of space and time. The Logos was with God in the beginning. In the beginning God created the heavens and the earth. Is it the belief of mainstream denominations that time began when the universe was created? Or did time begin when time keepers started keeping time that is to say when humans were created? Would time exist prior to physical creation? Doesn’t our counting of time rely on planetary movement? What does before time mean? Angels were on hand to applaud the foundation of the earth. Were angels created outside of time?