What is meant by "time keeps everything from happening at once"

From: Raymond E. Feist
Date: 14 September 2008

It's quantum physics, really.  The theory is before the Big Bang, time/space/everything was One Thing.  When it blew up, time was that property of Everything that ordered one dimension, what we think of as "the passage of time."  Without "time," everything would be happening simultaneously.

Best, R.E.F.