Well the relevance has to do with the amount of time that had transpired, for some it is a virtually inconceivable amount.<quoted text>
I do not see the relevance in your taking up so much space merely defining what the Cambrian explosion was, but to each their own.
While 5-10 million years is a virtually inconceivable amount of time for us, geologically it is not and when you recognize that mutation is virtually the result of the roll of genetic dice, most of which will not be successful, the amount of time reasonably required to result in the diversity found is staggering.
Course prior to the Cambrian Epoch there was still cellular life existing for thousands of millions of years, but it is the hard outter bodies of the Cambrian that left the hard evidence.
"the amount of time reasonably required to result in the diversity found is staggering."
And what would be the amount of time required, you offer no answer, how many generations of short-lived creatures are there in one year, or 100, or 100,000, or 1 million. As mutations creep into each generation, some beneficial and some not.
The hand of some nameless designer - god, wink-wink, nudge-nudge - is not required to propel events in a natural world.