Well Bocchiere would not have to worry about the barrier catching him off guard at least since it was plainly visible to the naked eye. At least according to the lack of detail stating otherwise in T'Challa's post.
Normally Bocchiere would call T'Challa out on nonchalantly poking through his Sage Mode enhanced body with one finger and say his attempt to activate the 8th gate failed. It's fun how that works as a fail-safe against people slapping buffs together without any real thought put into how they'd interact with each other. However on this particular occasion it would be quicker and easier to just allow T'Challa to kill himself with the 8th Gate, so that is what Bocchiere will do.
Seeing the movement the man made combined with his own knowledge of the Lotus through his associate Saejima, who himself was a master practitioner, allowed Bocchiere to know what T'Challa was about to do. Before the 8th Gate was fully activated Bocchiere would glance toward the peak of a mountain that was roughly 5 km behind T'Challa, he'd see it if he turned around to his left. Bocchiere would then instantly vanish and reappear on the peak of that mountain, facing the same direction he had been standing, though he would turn around to face T'Challa, seeing the glowing red aura surrounding him from even from such a distance and would allow the two Rasenshuriken he had been holding to disperse.
This was Bocchiere's unique technique that had been dubbed the Corridor of Infinity. It was a subject of his experimentation with Spatial Ninjutsu, a type of Ninjutsu that was also a unique invention of his. These techniques manipulated only space, not space and time, and so differentiated themselves from the much vaunted Jikūkan Ninjutsu. This also meant Bocchiere could teleport while under the effects of an enemy Anti-Jikūkan barrier, since the barrier was not equipped to handle his Spatial techniques. This of course meant that if the mystery barrier T'Challa had erected was an Anti-Space-Time barrier it would not have affected Bocchiere's teleportation (not that Bocchiere ever fell within its confines before teleporting away, anyway)
This technique functioned by allowing Bocchiere to create or delete an infinite amount of space (chakra pending) between himself and a second point in space. This meant Bocchiere could either delete the space between himself and a point to instantly teleport to that point, as he just had, or increase the space between himself and a point, to stop anything coming from that point from physically reaching him. The limitations of this (other than chakra of course) were that Bocchiere had to be able to physically see the second point (himself being the first) and it could only effect space in a straight line between himself and that second point.
Bocchiere of course cannot force T'Challa to concede but the fight is now basically over. Even if T'Challa claims to be able to cover the distance of 5 km before the 8th Gate kills him Bocchiere would have more than enough time to simply teleport to some other point some miles away, and continue to do that until the 8th Gate did finally kill T'Challa. The man would also not be able to stop the 8th Gate from killing him since he did not note that he had activated an Izanagi before opening the 8th Gate. If he had done so T'Challa could claim to die in less than the minute long timeframe of Izanagi (this assuming T'Challa had Senju enhanced Izanagi which his usage of Sharingan, Sage Mode, 8 Gates, and Ice Release shows he does not) would allow the man to claim to reappear prior to having activated the Gates. If he used Izanagi now he would merely appear moments before dying to the 8th Gate, only to die again, making the technique useless.
Bocchiere's bunshin would also vanish, returning its portion of his chakra to the original, since its presence was no longer needed.