So here's a very short version of what I have from 2 years of reading books and journal articles. About 6 million years ago there was an evolutionary split between hominids and apes. As you look at the various ancestors to homo sapiens, brain size increases although the time intervals are not equal nor are the volume increments.
There is a significant amount of literature describing the emergence of activities (wearing of jewelry, burials, art, etc.) associated with the development of modern cognitive capabilities. These activities do not appear in any straight time-line fashion, but arise in different places at different times with varying periods between their appearances. One all purpose tool sufficed for thousands of years. Development of multiple special purpose tools, once it began, was relatively rapid (at least in evolutionary terms) and continues today.
There are some studies by evolutionary biology/genetics people that attempt to determine when particular genes relating to the brain mutated. These studies give date ranges for when the mutations might have occurred. We share 96-98% of our genetic structure (I've read both numbers recently) with chimps.
In the cog psych literature the development of cognition appears to be equated with the development of language, but there does not appear to be a consensus on when language development occurred. I noted this in a paper I wrote last winter/spring - Dates for the advent of language, or symbolic references, range from 200,000 years ago with the expansion of the brain to modern human size and concurrent changes in vocal apparatus to five to seven million years ago during a period shortly after hominids and chimpanzees branched from a common ancestor.
If anyone is foolish enough to want to see the ever growing list of references, let me know.