Sometimes in the anime it would seem Erasehead have to be continuosly watching someone to erase their quirks, because if he stopped watching the target recovered his quirk, but in some of the episodes of the 4th season with Eri and with some of the villains from Overhaul's band it would seem that after watching them once their quirks got erased for a while.
Does Eraserhead have to be continuosly watching someone to erase their quirks?