There are no specific hours of paranormal activity. Paranormal activitiy means the phenomena that can be interpreted as ghost- and poltergeistphenomena.
There are several reasons, we say ghosts are more active at night:
- Usually, the haunting-hour was between 00:00 to 01:00. But now, as many people go to bed later, the hour has moved to 03:00 - 04:00. This hour is also called the "Witching-hour". And there is indeed a good reason for that. At that time, the human brain is most receptacle to hallucinations, and suggestion. ("Did you hear that!")
- At night, the senses are more acute. Therefore, we can feel small changes in light, sound, temperature and pressure.
- "Tradition": In all movies and TV-shows, paranormal activities are at night. This only deepens the mystery.