I read somewhere that the "day" for demon activity (which is what I believe the majority of paranormal spirit activity is), starts at 12 midnight, and that 3AM is "midday" for them, which seems to be the time they prefer to manifest on our plane of existence.
Probably because they prefer to remain hidden by the darkness, and most people are asleep at that time.
As far as not believing in Satan and demons goes, don't fool yourself, (or let Satan fool you), he's just as real as you or I, and so are demons. I can't prove this to anyone, but I know it for an absolute fact, for reasons I will never divulge. I couldn't care less if anyone believes me or not.
I know that everyone will believe someday, it's just a matter of mortality.
peace