Board Thread:Naruto Discussions/@comment-25122992-20161230113055/@comment-6036561-20161230165009

Maybe the summon contract is something akin to the hiraishin seals: you "teleport" near you someone whose exact location you don't know, and to do so you need some sort of link. That would be also why Hagoromo needed all the previous kage to summon team 7 & the bijuus from Kaguya's dimension: he knew where they were, but he didn't have the "link" with them, and so he neededa huge amount of chakra to do so. On Obito's case, what Minato disrupted was not the "contract" but the genjutsu control. On the time limit... I think we should consider it "retconned". I don't remember it being mentioned in Shippuuden, so I think that Kishimoto went back, on this