I'd be extremely easy to see during the day. -12 would be about as bright as the moon when 50% illuminated but only a point source. On a clear day Venus and Jupiter are relatively easy to spot if you know where to look.
Hint: Unless you normally have hazy skies, you want to try this when they're near the moon (ideally within the 7* FoV of a pair of 7x50 binoculars).
Re: The post on doomers.us appears to be engaging in massive brightness inflation
Hint: Unless you normally have hazy skies, you want to try this when they're near the moon (ideally within the 7* FoV of a pair of 7x50 binoculars).