TimeRiders: The Doomsday Code
February 03, 2011
In Chapter 9 of the third book in the series, Adam Lewis, a computer hacker in the Campus of the University of East Anglia, in Norwich, England, can hear his flatmates playing Mario on the SNES:
Since the console is the Super Nintendo and the scene takes place in May 1994, the game is most likely Super Mario World, also considering that the generic term "Mario" likely indicates a main game in the series. The only other SNES Mario games released at the time in Europe are Super Mario Kart, Mario Paint, and some educational games.
TimeRiders: The Eternal War
July 14, 2011
In Chapter 33 of the fourth book in the series, the Support Unit Becks recalls some memories, including playing "Mario Kart" with Liam and Bob on "the Nintendo":
Since it generically states "Mario Kart", and "Nintendo", it's unknown which specific Mario Kart game they were actually playing. The term "Nintendo" is often used for the Nintendo Entertainment System, but no Mario Kart games were ever released on the NES.
TimeRiders: City of Shadows
August 02, 2012
In Chapter 2 of the sixth book in the series, Maddy can hear Liam and Sal playing "Mario Kart" on "the Nintendo" in the archway:
Again, the book is not specific on the game or console played.
TimeRiders: The Pirate Kings
February 07, 2013
In Chapter 16 of the seventh book in the series, while working on a ship in the seventeenth century, Liam mentions "Mario Kart":
The writer nor the publisher of the TimeRiders novels held any right over Nintendo's Mario, but they only included minor references to the series.