Even if 10 seconds was the case (speculation btw), Kakuzu would only need to use it when he felt like he couldn't dodge an attack. Asuma and Kakashi dodged nearly all of Hidana attacks. Kakuzu was also a decent match against 3T Kakashi so I believe he could dodge most if not all his attacks. Also, either Kakuzu could fight Hidan 1 v 1 or 5 v 1 via the "fodder" masks (they do kinda suck). Hidan can't fight all 5 of them at once especially while trying to kill Kakuzu, he just isn't that skilled. Against an opponent like Hidan, you don't kill, you make in capitate your opponent to where they can't fight back (Hidan/Shikamaru fight). To wrap it up Kakuze can use his mass of tendrils to grab Hidan and cut off his legs, arms, or head after wearing him down with his 5 masks and defending himself with his iron skin and reflexes.Kakazu can't use iron skin for long probably only max 10 seconds man.
Or else why not spam in his fights?
EXACTLY
And you said it yourself you can't kill hidan.
Kakazu just has nothing in his arsenal so he makes it seem like he is stronger.
Hidan endures all of kakazus attacks and we all know kakazus hearts are pretty fodder man.
Kakashi took em all out
Part 2 kakashi 3 tomoe