Besides "Stars are not right" and "Stars are right" basically means "Things haven't come into place" and "Things have come into place" rather then literally meaning that Cthulhu lives and dies according to the movement of the stars themselves.
I'd argue the quote posted by Bohandas:
These Great Old Ones, Castro continued, were not composed altogether of flesh and blood. They had shape—for did not this star-fashioned image prove it?—but that shape was not made of matter. When the stars were right, They could plunge from world to world through the sky; but when the stars were wrong, They could not live. But although They no longer lived, They would never really die. They all lay in stone houses in Their great city of R'lyeh, preserved by the spells of mighty Cthulhu for a glorious resurrection when the stars and the earth might once more be ready for Them.
Strongly suggests that it is not the idiomatic "things coming into place", but a very literal case of Cthulhu basically being dead without being properly dead when the stars are normal and a transplanar awakened god-being "plung[ing] from world to world through the sky" when they are "Right", neither of which is entirely the case in CoC.
I definitely see "the stars are right" as a very specific apocalyptic event in the Lovecraft universe, a literal astral alignment that awakens Cthulhu and his fellow star-spawn, rather than an idiom for "when the time is right".