JANUARY
BATMAN ADVENTURES HOLIDAY SPECIAL #1 is released (1995)
BATMAN ADVENTURES #28 is released (1996)
10th-THE LAUGHING FISH premiers (1993)
16th - MAD LOVE the episode - premiers!! (1999)
18th - HARLEY AND IVY - the episode that teamed the gals up!!(1993) 

FEBUARY
BATGIRL ADVENTURES #1 is released (1998)
1st - THE MAN WHO KILLED BATMAN premiered (1993)
the month that "MAD LOVE" was published and released!!yay!!(1994) 

SPRING
- First eva Elseworld Harley makes her debut in THRILLKILLER '62 oneshot.

MARCH
The month that saw the release of "THE DARK KNIGHT RETURNS" - the comic in which the Joker dies.(1986) 

APRIL
Batman #1 is released - and THE JOKER IS BORN! (and he dies. But then he comes back to life again!!) (1940)

MAY
BATMAN AND ROBIN ADVENTURES #18 is released (1997)
16th - TRIAL premiered (1994)
Batman debutes in "Detective Comics 27" in "THE CASE OF THE CHEMICAL SYNDICATE"(1939)
23rd - Harley's first solo episode - "HARLEQUINNADE" (1994) 

JUNE
Poison Ivy is born in "Batman #181" in "BEWARE OF...POISON IVY!"(1966) 

JULY
BATMAN AND ROBIN ADVNETURES #8 is released (1996)

AUGUST
"Harely Quinn" the comic that introduces Harley into the mainstream continuity is released! (1999)
The month that The Haven of Hedonism was officially completed (as it was then) and made known to the world of Bat Fans! (1997) (ok so it's not that important but I couldn't have august EMPTY!)

SEPTEMBER
11th - HARLEY IS BORN!!WHOPPEEEEEE!!!!!(1992) 
(Note: This is the day the first ever appearance of Harley in "Joker's Favour" took place, therefore it is generally acknowledged and hailed as her birthday, although her conception and design would've taken place months before)

OCTOBER
14th - Arleen Sorkin's B-day!!YAY!!(1956) 

NOVEMBER
BATMAN AND ROBIN ADVENTURES #1 is released (1995)
6th - The Unofficial Harley Quinn Fan Club is founded, by her numba one fan, ME(1997) 
11th- ALMOST GOT 'IM - Harley's second appearance premiers (1992)

DECEMBER
a "DEATH IN THE FAMILY" runs - where Mistah J murders Robin!! (1988)