From another thread here, on how evolutionists calculate such dates:
http://www.jehovahs-witness.net/jw/friends/46578/6/DNA-and-Mans-origin
To estimate the time when the most recent ancestral sequence common to the Neandertal and modern human mtDNA sequences existed, we used an estimated divergence date between humans and chimpanzees of 4–5 million years ago and corrected the observed sequence differences for multiple substitutions at the same nucleotide site. This yielded a date of 550,000 to 690,000 years before present for the divergence of the Neandertal mtDNA and contemporary human mtDNAs. When the age of the modern human mtDNA ancestor is estimated using the same procedure, a date of 120,000 to 150,000 years is obtained, in agreement with previous estimates. Although these dates rely on the calibration point of the chimpanzee-human divergence and have errors of unknown magnitude associated with them, they indicate that the age of the common ancestor of the Neandertal sequence and modern human sequences is about four times greater than that of the common ancestor of modern human mtDNAs.39