[{quoted}](name=Loken Stoneheart,realm=NA,application-id=3ErqAdtq,discussion-id=qz7W6ZZV,comment-id=0000,timestamp=2015-03-12T01:57:29.270+0000)
Lasts for .75 seconds.
According to the 5.5 notes, its down to .50 seconds in addition to the warning particle now appearing at the start of the animation (rather than the end)
E - Event Horizon
DELAY BEFORE WALLS APPEAR 0.75 ⇒ 0.5
WARNING PARTICLE DISPLAY After cast time ⇒ On cast
Interesting because the former of the two changes wasn't on the PBE (though its not the first time something has happened without ever being on the PBE)
The dash-stopping effect will be on as well (confirmed that it was supposed to be on as well, but was pulled until 5.6 due to a last minute bug)
Edit: As a quick comparison between the 3 versions of Veigar's E stun delay
Pre 5.4: .25 seconds
5.4: 1 second
5.5: .50 seconds