1. He didnt just clap his hands. In the scan before he jumps back to perform the handseals needed.
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which are once again
Tiger → Snake → Dog → Dragon → Clap hands
Then the coffins also appear one by one. slowing it down even further.. This is even evident in the scan you posted.
"When first summoned, the body of the reincarnated is stored in a coffin; their body will appear grey and in a state of minor "decay": marred by cracks and other imperfections, and the individual will also appear to be "disengaged".
courtesey of naruto pedia.. So this means out of the box they are not even ready to fight.
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Kabuto has to give them a command to do so. He has to activate the corpse then either decide to control it or let it have free will. taking up even more time.
Now back to the top. Kabuto had to make space to use his signs. this jutsu is offensive as soon as the snake sign is waved.
Here one sign: Snake
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While kabuto is waving his signs hashirama is already done. when he completes his signs this is happening here
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He is being hit by wood style even before the pollen is a factor. all of this is happening either while he is still waving signs, or the coffins are appearing. he has yet to give an order to the edos yet to even fight.
and the scan you didnt post would be here
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holding your breathe that effective???
No.. not effective. they only reason they did not succome sooner was because gaara had them elevated above the pollen. kabuto cannot fly so he would then still be on the ground. and just like the kage he would be sleep.
It does not matter why madara broke free your giving him an excuse. he was never under kabuto's control. there is no scan where he is so this is never the case.
So
Holding your breathe obviously wont work forever.
Edo tensei is slower and the caster can be struck before he is done waving signs if the mokuton jutsu is used at the same time as edo tensei.
Without flight or a jutsu to destroy the flowers and the pollen your screwed.
Edo tensei has steps you dont just clap and they are ready to fight. the jutsu is not as instant as you make it seem.