“24/7” usually means 24 hours a day, 7 days a week—all the time. “22/7” is an approximation for the number π (“pi”).
 
“There’s a new shop only sells Pies it’s open 22/7” was posted on Twitter by Martin Topping on May 11, 2011. “There’s a new pie shop near me. It’s open 22/7” was posted on Twitter by The Dad Joke Man on April 20, 2019.
   
     
Wikipedia: Pi
The number π (/paɪ/) is a mathematical constant. Originally defined as the ratio of a circle’s circumference to its diameter, it now has various equivalent definitions and appears in many formulas in all areas of mathematics and physics. It is approximately equal to 3.14159. It has been represented by the Greek letter “π” since the mid-18th century, though it is also sometimes spelled out as “pi”. It is also called Archimedes’ constant.
 
Being an irrational number, π cannot be expressed as a common fraction (equivalently, its decimal representation never ends and never settles into a permanently repeating pattern). Still, fractions such as 22/7 and other rational numbers are commonly used to approximate π.
   
Twitter
Martin Topping
@eMartinTopping
Replying to @RobinFlavell
@jacques_aih “There’s a new shop only sells Pies it’s open 22/7” - was that you?
7:39 AM - 11 May 2011
   
Twitter
Rofl Republic
@i_theindian
The pie shop in my neighbourhood hardly closes. It’s open 22/7.
9:15 AM - 13 Jan 2014
     
Twitter
Peter Coles 🌈  🇪🇺  🇮🇪
@telescoper
My new business venture is a shop selling approximations to pi. It’s open 22/7…
4:27 PM - 19 May 2017 from Cardiff, Wales
   
Twitter
Mark Haggan
@markhaggan
More Mark Haggan Retweeted Chris Mason
My local pi shop almost never closes. It’s open 22/7 Mark Haggan added,
Chris Mason
@ChrisMasonBBC
(A sign, “PRIVATE MATHS TUITION AVAILABLE 25/7.”—ed.)
3:23 PM - 23 Jun 2018
     
Twitter
Stottiez
@stottiez
Replying to @cals_own
Perhaps we should open a restaurant called Pi, we can decide on the menu later, but I insist it’s open 22/7…
1:05 PM - 14 Jan 2019
 
Twitter
🤣 The Dad Joke Man 😉
@DadJokeMan
There’s a new pie shop near me. It’s open 22/7…
12:43 PM - 20 Apr 2019