Turnip Time Machine is a time machine that Timmy Turner wished up to travel back in time during the episode, Timmy Turnip.
Because of Timmy Turner's wish that his grandparents never left Ustinkistan, he ended up living in the impoverish country and everything about his life was changed, including Cosmo and Wanda who could now only grant wishes involving turnips. So Timmy wished for a Turnip Time Machine so that he could travel back in time and convince his grandfather Grandpa Vlad to go to America with his wife Grandma Gladys and start up their Yak in the Box restaurant chain like they did before Timmy granted the wish to prevent them from leaving.
The time machine is shaped like a giant turnip. It sprouts from the ground after Timmy's fairies grant his wish. The turnip sparks with blue energy as it is activated, then spins really fast and tunnels into the ground. The turnip then emerges from the ground in the new time period. When Timmy steps out, he believes the machine didn't work because Ustinkistan is exactly the same, until he sees his younger grandparents.
This is the second time machine Timmy wished for after the Time Scooter.