Yes, the generation time is a parameter in models of evolution. The first reference by Hobolth is an example of this. Because of the range you mentiond, one needs some sort of average. But what sort of average? Some of the problems are discussed in the second and third references. (In the PubMed links, there are links to free versions of some of these articles at the top right of the page)
Hobolth A, Christensen OF, Mailund T, Schierup M. Genomic relationships and speciation times of human, chimpanzee, and gorilla inferred from a coalescent hidden Markov model.
PLoS Genet. 2007 Feb 23;3(2):e7.
Tremblay, Vezina. New estimates of intergenerational time intervals for the calculation of age and origins of mutations.
Am J Hum Genet. 2000 Feb;66(2):651-8.
Kim SH, Elango N, Warden C, Vigoda E, Yi SV. Heterogeneous genomic molecular clocks in primates."
PLoS Genet. 2006 Oct 6;2(10):e163.