- Becomes Batman in Begins, we'll say he's active for a month (even though the Scarecrow, Ra's, Falcone, LoS thing is probably a couple of weeks)
- Dark Knight is 8 months later (newly elected Dent replacing Finch, Joker still bank robbin')
- The Dark Knight story is in the span of a couple of days (bank robbery, party, Hong Kong, etc.)
- Then according to TDKR, he retires the night he takes Joker and Two-Face down
So you have a 9 to 10 month old Batman before he retires. Then he comes back after 8 years in TDKR, for like two nights, then is out of commission again, thrown into a pit. Then he comes back for literally a day (there's only hours left till the bomb goes off) then ends his career permanently and quits for good.
11 months, if we're being generous. To make matters worse, Scarecrow's criminal career is a little longer than Batman's and Joker doesn't even clock in a month with his time as the Joker before he's silenced completely. Also Two-Face is literally the span of a day and a half before Batman kills his ass.