A very recent speciation time of human-chimp

Hobolth A, Christensen OF, Mailund T, Schierup MH (2007) Genomic Relationships and Speciation Times of Human, Chimpanzee, and Gorilla Inferred from a Coalescent Hidden Markov Model. PLoS Genet 3(2): e7

They estimate 4.1 million years ago. It’s open access so no excerpts needed.