I'm currently reading The Dark Knight Manual: Tools, Weapons, Vehicles and Documents From The Batcave.
Cool book, written in the first person (Bruce Wayne) and there's a reference to the first five years as Batman.
This tells me that Batman operates for a few years before that year he spends going after the upper echelons of organized crime, the year the Joker refers to in TDK. That backs up a reference in TDKR about Bruce's "years" as Batman. The idea seems to be that Bruce was Batman for at least five years from BB to the events of the TDK. Also we don't know how long he operated as an outlaw after the events of TDK. In TDKR it merely makes a reference to eight years since the last confirmed