well that kinda how i said it... but no dummy unit which get moved by a timer... just set the day sight to what u want and a small trigger, when it pick up the flash light add upgrade ultravision to the player with the flashlight and when he drops it remove the upgrade(dunno if removing is possible) if not possible make it undropable. this is the best and simplest way to do it
p.s this shouldnt work on the day like who use a flashlight on the day? :>