Board Thread:Naruto Discussions/@comment-25977287-20150704114842/@comment-25977287-20150705001232

Tasuxeda wrote: In my opinion, Minato took advantage of Madara being distracted by Obito to gather natural energy while Madara was talking, so it isn't that Minato entered sage mode instantly but he preparing to use it since Madara appeared. False.

We saw Minato throw the kunai at madaras feet before entering sage mode, which means Minato moved. If you move even a little while gathering nature energy, then entering sage mode will fail. As Fukasaku said, it's physically impossible to move whole gathering nature energy.

So obviously Minato entered sage mode the very instant after he threw that kunai. There was is no other explanation. His eyes only changed after that kunai was thrown,meaning sage mode was activated right ere and then.