Because no matter what local church you are at, no matter what time is noted above the "attempt at humor but often highly inappropriate and offensive" sign outside your church building (can we get rid of this please!), worship does not begin at 11am.
Worship began eons ago and we just happen to join in that ongoing worship at 11am on Sunday.
If we were to meet at the river at 11am and jump in for a swim, our actions did not "start" the flow of the river. Rather the river has been there long before and will be there long after our actions.
We just join into the flow of it for a time.