From Wiktionary, the free dictionary
wine o'clock (uncountable)
- (slang, humorous) The time of the first glass of wine (or alcoholic beverage) of the day.
2000 August 31, The Evil Queen [username], “Re: Where ya from?”, in soc.subculture.bondage-bdsm.femdom[1] (Usenet):(mm - how long till wine o'clock? Damn, I think it's still about 3 or 4 hours!)
2014, Binki Laidler, Staying Sober: How to Control the Drink Demon[2], Accent Press, →ISBN:Then I'd spend Saturday a bundle of hangover nerves, waiting for Saturday wine o'clock to make it disappear.
2014, Belinda Williams, The Boyfriend Sessions[3], Momentum, →ISBN:Thank God it was wine o'clock.
I gulped, rather than sipped my glass of wine, then fell back in the armchair.