What is the opposite of a false dawn, a false dawn being "a promising situation which comes to nothing". The sentence I'm thinking of would be something like: They started off well and it was not a false dawn it was ...?
Resplendent sunrise of good fortune
The day began full of promise, and it was no false dawn, but rather a resplendent sunrise of good fortune. They met his price, and his commission check was as good as in his pocket . . .
Perhaps "bona ﬁde daybreak" might work for you.
Google finds a hint that this has all been done before: "Apple, along with Windows 7, is busily ensuring that this false dawnbecomes (sic) a bona ﬁde daybreak".