"Whiskey Wednesday” is a drinking slang name for a day of the week. Whiskey drinks are sold on this day, often at a reduced price. “Whiskey Wednesday” has been cited in print since at least 1977.

Other slang names for days of the week include Shunday, Sober Sunday, Margarita Monday, Messed-up Monday, Mojito Monday, Moonshine Monday, Boozeday Tuesday, Tanked Tuesday, Tasty Tuesday, Tequila Tuesday, Tipsy Tuesday, Trashed Tuesday, Twisted Tuesday, Wasted Wednesday, Wine Wednesday, Winesday Wednesday, Thirsday, Thirstday, Thirsty Thursday, Fucked-up Friday, Shit-faced Saturday, Sloppy Saturday, Sloshed Saturday and Smashed Saturday.


11 November 1977, The Plain Dealer (Cleveland, OH), pg. 22, col. 1 ad:
WHISKEY WEDNESDAY
(Pirate’s Cove—ed.)

LiveJournal
Chris Knehans (nebsoldier) wrote,
2000-07-13 13:04:00
Days of the week
Below is my interpretation of the days of the week:
Monday = Malibu Monday
Tuesday = Two fur Tuesday
Wednesday = Whiskey Wednesday
Thursday = Thirsty Thursday
Friday = F***ed up Friday
Saturday = Sloppy Saturday
Sunday = Sobering Sunday
Yes sunday is our day of rest...why? Because God said so.

New York (NY) Times
STYLE & ENTERTAINING; Whiskey À Go-Go
By William Norwich
Published: October 06, 2002
(...)
Hopey even entertains at home—on Wednesdays, about once a month, in a sort of easy, breezy salon she calls Whiskey Wednesday. Simple stuff: a few bottles of whiskey, small groups of chums and if there is enough money, or everyone chips in, some take-away food from Rice, owned by her friend David Selig, on Mott Street nearby.

OCLC WorldCat record
Making enemies
Author: Minor Times (Musical group)
Publisher: [Philadelphia] : Level-Plane, 2004.
Edition/Format: Music LP : Rock music : English
Contents:
The pugilist at work --
Old world vulture --
The narcissist at rest --
Whiskey Wednesdays --

San Diego (CA) Citybeat
Wednesday, Dec 06, 2006
Off at 5, happy by 6
A review of some swanky spots
By Candice Woo
(...)
Out on Harbor Island, C Level Lounge‘s happy hour may be difficult to catch if you’ve got a 9-to-5 job since it ends at 5:30 p.m., but if you can play hooky, you’ll be rewarded with $5 appetizers including ahi tuna poke, fried calamari and a molten-centered, nut-crusted brie. A five spot will also get you a drink special, which varies throughout the week. Whiskey Wednesday is my favorite day, but Mojito Monday comes in a close second.

OCLC WorldCatrecord
Alabaster room
Publisher: [Connecticut] : Chrissy Gardner, 2008.
Edition/Format: Music CD : CD audio : Popular music : English
Contents:
Alabaster room --
Little Adahy --
Summer riff --
Where she goes --
Mother come quickly --
Whiskey Wednesday --

7 February 2008, Austin (TX) American-Statesman, “Austin 101,” pg. T16:
And because karaoke without a healthy amount of booze is like Hall without Oates, Common Interest offers a variety of weekly specials, including Tecate Tuesday, Whiskey Wednesday and Thirsty Thursday.