One question we need to ask about the question of time is what sort of process leads to each breakthrough.
Is it more like buying a lottery ticket with every generation, or is it like saving until you have enough money to buy the next step?
It may well be that the Cambrian explosion was the result of 3 billion years of small improvements and would have been impossible at 1 billion years.
The history of invention in human history seems to work more like savings -- as soon as sufficient progress has been made, the breakthrough happens independently.
There's a problem in independent invention in evolution as well--once the first evolution takes place that niche is occupied. An independent invention may be beat out for resources by the more polished first-mover. Short-lived species leave very few fossils.
The problem with Cambrian explosion is that it seems to have occurred in way too many separate lineages simultaneously. The most recent common ancestors for animals from Cambrian explosion seems to be go quite far back (that however is another controversial issue, molecular clocks are always controversial), and then suddenly all at once multiple independent lineages undergo period of extremely fast evolution. It's a problem unresolved since 19th century. Wikipedia - Cambrian explosion
We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.
Major types of hints are:
Data for:
Data against:
To me it looks like life, animals with nervous systems, Upper Paleolithic-style Homo, language, and behavioral modernity were all extremely unlikely events (notice how far ago they are - vaguely ~3.5bln, ~600mln, ~3mln, ~200k or ~600k, ~50k years ago) - except perhaps language and behavioral modernity might have been linked with each other, if language was relatively late (Homo sapiens only) and behavioral modernity more gradual (and its apparent suddenness is an artifact). Once we have behavioral modernity, modern civilization seems almost inevitable. Your interpretation might vary of course, but at least now you have a lot of data to argue for your position, in convenient format.