1981 to about 1988.
According to this article, the public announcement about the FBI adopting the 3 inch Model 13 was "last summer," which would make adoption sometime during 1981. See page 32:
http://www.americanhandgunner.com/1982issues/HMJ82.pdf
After the Miami shootout in 1987, FBI briefly went to SIG 9mm pistols using the OSM load (Olin Super Match) until the ammo testing protocols were developed and a cartridge and pistol were selected to replace the issue revolver. The SIG 9mm/OSM load was a "stop-gap" until adoption of the 10mm and the S&W 1076.