Completely agree! Though time travel wasn't a MacGuffin, it was just a plot contrivance. A Macguffin is an interchangeable irrelavent object used to drive the motivation for the plot. The "tesseract" in Avengers, or the "Philosopher/Sorcerer's Stone" in Harry Potter for example.

Sorry to be pedantic, I fully agree with your actual point, and just thought you might want to know.