I don't trust anything that has reached the stage where it more or less looks like a miniature adult, which is what most people consider hoppers to be. Most of my snakes take food before it hits the bottom of the tub, but whether rats or mice, I only leave them in for an extended period of time if they are at the point where their eyes are just barely opening, or recently opened within a day (at this stage, they also still seem to have problems with mobility). I've seen what tiny mice can do to tiny snakes... and they are not to be trusted alone with your snake