Quoted:
Use the lens cover with the pinhole during the day and be as quick as possible, preferably covering the pinhole after each shot while making adjustments.  At night, there are a few different techniques that can assist you in finding your zero.  My old reliable version is to insert an IR chemlight through a piece of cardboard with one end just sticking out of the face of the target enough to hold it steady. As you dial in the NV scope, the holes will be backlit by the chemlight and when you've exploded the chemlight you've got your zero.