Considering Backmasking’s main use it to Rewind magic circle duration, i suggest making backmasking animation and effect be almost instantaneous.
Right now it takes slightly more than 1 second to be cast, and considering the entire skill is meant to be used to rewind duration of magic circles when they are about to expire, being able to use it on the very last moment to double the duration would feel more amusing and meaningful than having to use it 1-2 seconds beforehand just because the animation takes too long.
Thanks for your attention.