The common wisdom is that they will drop during the small hours as has already been said, but they may also drop during the day. There is no hard and fast rule.
As for breeding traps, I have often looked on in boredom whilst the merits and demerits of them have been extolled. The truth is that there is so much crap spouted either way that you just have to work it out for yourself.
Steady has worked it out for himself and he thinks they are great, I have worked it out for myself and I have another view; if traps work for you then go for it, if not then do something different. There are loads of options, from the simple to the elaborate.