e1 - Evidence for Gil Grissom joining CSI in 1986:
According to Gil's bio, he was the "youngest coroner in the history of L.A. County at age 22. Eight years later, a headhunter recruited him to run the Field Services office in Las Vegas". Therefore, he would have joined CSI when he was 30, between August 17, 1986 and August 16, 1987.

e2 - Evidence for Catherine Willows joining CSI in 1987:
According to Cath's bio, she "worked as an exotic dancer on the Strip in her early 20s while going to college. A young [field] services officer named Grissom recruited her to work at the lab. She started as an assistant technician". This would indicate that Gil recruited her to join the lab right out of college, when she was about 22 years old, or between March 26, 1985 and March 25, 1986. Since it is estimated that Gil joined the Vegas lab not before August 1986 (e1), he could not have recruited her before then, so she was probably recruited when she was between 23 and 24 instead.

e3 - Evidence for Jim Brass joining CSI in 1990:
According to Jim's bio, he "transferred out of Homicide and out of New Jersey 10 years ago and came to Las Vegas. He eventually came to run the CSI department, more as an administrator than as an investigator". If the bios are set at the beginning of the series, which was originally aired in 2000, this would indicate that Jim moved to Vegas and joined the LVPD in 1990.

e4 - Evidence for Catherine Willows becoming a CSI 1 in 1994:
According to Cath's bio, she "worked her way up over a decade to become a CSI level Three". If she began in 1987, this means that she was a CSI 3 by 1997. Based on the estimated three years it took Nick Stokes to become a CSI 3 (e11), Catherine would have become a CSI 1 approximately 4 years before becoming a CSI 3, which puts her as a CSI 1 in 1994.

e5 - Evidence for Nick Stokes being a Dallas police officer in 1994:
According to Nick's bio, he "spent his first three years out of college on the Dallas police force". If he graduated when he was 22, as most Americans attending 4-year universities do, that means he was a police officer from (approximately) summer 1994 to summer 1997.

e6 - Evidence for Sara Sidle being a grad student in 1994-1995:
According to Sara's bio, she "attended graduate school in theoretical physics. Worked in the San Francisco coroner's office for five years, then transferred to the San Francisco crime lab before being contracted by Gil Grissom to come to Las Vegas". Since we know she joined LVPD in 2000, and the five years at the coroner's office must have been from 1995-2000, the only time she could have been a graduate student would have been in 1994-1995.

e7 - Evidence for Doc Robbins joining CSI in 1995:
According to Doc's bio, "he has been the chief medical examiner in Las Vegas for the past five years". If the bios are set at the beginning of the series, which was originally aired in 2000, then Doc has been the chief medical examiner since 1995.

e8 - Evidence for Warrick Brown joining CSI in 1995:
Warrick's bio is disappointingly vague. Fortunately, evidence can be found from another source: the show itself. In $35K O.B.O., which originally aired on March 29, 2001, Warrick says quote: "Six years on the job and it still freaks me out in here" (referring to the drying room, whatever that is). That puts Warrick joining the LVPD some time around the beginning of 1995.

e9 - Evidence for Warrick Brown being an audio/visual tech in 1995:
According to the projections for Warrick's career, he began at CSI in 1995 (e7). He probably wasn't a CSI to begin with, unless it took him almost two years longer than Nick to earn his CSI 3 status (briefly, Warrick and Nick became CSI Level Threes in 2000 [see Pilot and Pledging Mr. Johnson] and it is estimated that Nick became a CSI 1 in 1997 (e12)), which is unlikely given his skill level. There is evidence that Cath started as a technician before becoming a CSI (e2), and Greg was a DNA technician until he became a CSI in 2004 (see any episode from the first four seasons).

So between it not being likely that he took two years longer than Nick to become a CSI, and other CSIs being technicians before they were CSIs, Warrick probably started as a tech. He was probably an audio/visual technician because a) someone had to do that job before Archie showed up, and b) according to Warrick's bio, his special skills are in audio/visual analysis. That can't have come from his bachelor's degree in chemistry.

We also know from Chandra Moore in Viva Las Vegas that Warrick gave a presentation on "longitudinal striations of the toenail" for the American Academy of Forensic Sciences in Dallas (on a side note, did Nick possibly see and meet Warrick at this conference while he was a cop in Dallas, and is this the connection that brought him to Las Vegas, in the same way that Gil is the connection that brought Catherine and Sara to the LVPD?). The forensic application of striations of a toenail is a visual analysis, further supporting the possibility that Warrick began his career at CSI as an audio/visual tech.

e10 - Evidence for Sara Sidle being a coroner's assistant in 1996:
According to Sara's bio, she "worked in the San Francisco coroner's office for five years, then transferred to the San Francisco crime lab before being contracted by Gil Grissom to come to Las Vegas". Since we know she joined LVPD in 2000 and she transferred immediately after being in the San Francisco coroner's office, she would have been there from 1995-2000.

e11 - Evidence for Warrick Brown becoming a CSI in 1997:
We know that Warrick and Nick became CSI 3s at the same time in 2000. Their skill levels are similar, so Warrick probably became a CSI 1 at around the same time Nick did, and that is calculated to have occurred in 1997 (e12).

e12 - Evidence for Nick Stokes becoming a CSI in 1997:
According to Nick's bio, he "spent his first three years out of college on the Dallas police force, then transferred to the Dallas crime lab, spending one year as CSI Level One". If he spent his three years as a Dallas police officer from 1994-1997 (e5), then he must have become a CSI Level One in 1997.

e13 - Evidence for Greg Sanders being an intern in San Francisco 1997-1998:
According to Greg's bio, he "interned as an entry-level lab tech at San Francisco PD for two semesters". Since this was an entry-level internship, it was probably something he did after college, not during. If he graduated college at 22 years old in 1997, then those two semesters had to take place somewhere between summer 1997 and summer 2000 (three years). It is possible that he took a break between school and getting a job, but since we know that Greg has been a motivated scientist since the age of seven, it's likely that he joined the work force right out of college.

e14 - Evidence for Nick Stokes joining CSI in 1998:
According to Nick's bio, he spent "one year as CSI Level One before transferring to Las Vegas". According to the estimate that Nick became a CSI in 1997 (e5, e12), it follows that Nick would have joined the LVPD as a CSI in 1998.

e15 - Evidence for Greg Sanders joining CSI in 1998:
Greg's bio is more vague than Warrick's in this matter. Based on estimates of when he went to college and the year he spent interning in San Francisco (e13), Greg had to have joined CSI some time between 1998 and 2000. Given Greg's career goals ("You can almost smell Quantico, you know?"), he probably didn't put it off.

e16 - Evidence for Sara Sidle joining CSI in 2000:
Sara is brought in to investigate Holly Gribbs' death and Warrick Brown's involvment in the second episode, Cool Change, which originally aired on October 13, 2000.