If cost is an issue, choose a weekday night and an early time slot.
If you're after more scary times, once its dark its dark ! Contrary to some beliefs it does not get darker as the night draws on. However, darkness is affected by the cloud cover and the moon's phases. The cloud cover will be what it is on the night. The moon is least bright when it is new (15th October 2012) and brightest when it is full (29th October 2012) but its brightness can be almost entirely dimmed by cloud cover.
