Board Thread:Naruto Discussions/@comment-25977287-20150704114842/@comment-25467892-20150705022605

Another thing to remember is that Minato, in spite of his admitted lack of skill with Sage Mode, was low on chakra at the time. He was balancing his own energy with Sage energy, but he had very little of his own chakra left. That means he probably didn't need to gather that much senjutsu chakra in in order to perfectly balance it with the little chakra he had, that would let him enter a weak Sage Mode pretty fast because he didn't have a lot of energy to balance.