What are the Big Bang assertions/assumptions about the speed of light and the mass of the universe in the first 1 second of the "event"?
I think you've mistaken me for a "big bang" theorist. I have not said I was and don't claim to be.
So what happened 1 nanosecond, or 2 hours, or 5 years after the universe was initially formed is something I know nothing of, nor do I much care about.
How the universe got started (whether creation or big bang or some other way) is open to faith, assumptions, scientific theories, etc.
What is not open for debate is that the universe is at least 10 - 15 billion years old. And what is not open for debate is that the speed of light has been established and verified at 186,000 miles per hr.