I personally feel there is no reason to stun a mouse.
Drop in mouse and come back a little while later. If mouse is still present, remove mouse. I don't think you have to worry about a mouse ripping apart a snake in 5 minutes. That kind of thing usually happens overnight or even longer.
You're wasting your time "stunning" the mouse and I personally think it's cruel, it is not a quick clean kill, you're bludgeoning the little thing.