Nautilus' passive is checked at on-attack declaration rather than on-attack launch

Much like teemo's blind (fixed in 5.7) Nautilus' passive counts from the time that you start the attack rather than the time that the attack hits. the passive says the effect cannot be used more than once every 7 seconds, but really it's more like 7.5 seconds.

the difference between 7s and 7.5s isn't a big deal, but the indicator around the enemies which shows when you can use the effect will sometimes be completely gone, and the stun will not hit because you started the autoattack slightly before it was gone.