Originally Posted by apacolypz
Yeah it is as I said during the fight with Minato he knew very well what FTG was. I thought Kael meant during the Kakashi Gaiden arc.
The Gaiden took place less than a year after Obito was crushed. The entire time during the Gaiden, the only opportunity Obito had to see the markings was on the kunai Minato gave to Kakashi. The seal was never explained while Obito was part of the group (Minato explained the markings when Kakashi woke up after the cave-in). When Minato took out the first enemy ninja that he rescued Kakashi from, the seal was on the guy's foot and Obito was blinded by tears.
As I said, it was only when they fought that he figured out the markings. He didn't know how Minato's FTG worked until then. All he knew was that Minato was extremely fast, and Rin even believed FTG was just Minato's Shunshin (mentioned to Obito/Kakashi when Minato teleported to kill the first guy).