Minato's striking speed is instantaneous or close to it anyway. There is practically no lag between the teleportation and striking speed at all. If you look carefully at these pictures:
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you'll notice that the kunai's position didn't change at all(while still in motion like we can see the straight lines indicating that on the second picture) when Minato teleported and striked Obito's back.
Now why didn't it perfectly work against Jubi jins(well more like against Madara jin considering even Obito jin had troubles)? It's because they possess high level precognition sensing(Rikudo chakra increasing that perception to extremes unlike the normal sage mode danger sensing Kabuto or SM Naruto showed for example) allowing them to predict attacks a certain while in advance and defend/counter-attack accordingly. Naruto himself(the best sage sensor of this manga) could notice Kaguya's teleportation movement the first time he actually saw it before everyone else and before the action actually happened(bottom right panel):
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Not to mention in the Minato-Madara's case, Minato didn't actually directly teleported onto Madara but some place before him from a kunai just placed right before him some time before. So not only he(like any other) could have actually easily anticipated the teleportation(since the kunai was throwed right before him a second before) but he also had his high precognition sensing active.
This is Naruto's six path sage mode databook
Notice the bolded emphasize Madara Jin's reaction speed from
the height of his sensing ability(and Naruto's exceeding his own)
Usually when hiraishin users teleport, you can notice question marks(whether from partners or foes):
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In Jubito's case, he was even prepared for any hiraishin teleport on his back(the chakra arms created as an auto-defense), yet he still had the surprised teleportative moment before actually defending himself:
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But notice Madara had no question mark when Minato teleports:
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It was practically like he was waiting for it(most likely due the the height of his sensing ability along/with kunais anticipation)