Well... You can just remove the aura during the night and add a dummy ability.
Event - Every 0.10 seconds Conditions - time of day is greater than 18 or less than 6 and Number Of Units within (Playable Map) Matching(Level of YourAbility for (Matching Unit) greater than 0) Actions - Pick Up Every Unit within (Playable Map) Matching(Level of YourAbility for (Matching Unit) greater than 0) and do actions - Remove YourAbility from (Matching Unit) - Add DummyAbility for (Matching Unit)
During the day you invert things. You check for the DummyAbility and remove it from units, adding YourAbility. And as for the condition for time of day as day -