There is no correct answer - only other's experience. On same day any number of things could go wrong and you'd lose your long haul.

It's all dependant on the level of risk you're comfortable with. I flew to MAN at approx 18.00hrs for a MAN-DOH-AKL leaving at 21.30hrs. I cut it too short and I spent too long worrying about it in the lead up. All worked out fine - but it could have gone awfully wrong