false dawn

noun2

1. •
   A thin ambient light which precedes true dawn, typically by around an hour, in certain parts of the world.

   • The moon was low down, and there was just the glimmer of the false dawn that comes about an hour before the real one. — 1888
2. •
   (figurative) Something engendering premature hope; a promising sign which in fact leads to nothing.

   • As Congo nears the 50th anniversary of its independence from Belgium on June 30th, Mr Chebeya’s murky death suggests that 2006 was a false dawn. — 2010