I would rather say go with your guts, and how well you are prepared. If you have done your pre-launch homework well, go anyday. If not, then firstly have your ammunition set.
Worst time - definitely holidays. As for best time, it depends on your goal:
If you want to maximize traffic, aim for Tuesday/Wednesday/Thursday.
But if you're hunting for badges, Friday and weekends can work better - less competition those days