Evidently that answering to the headline you can say that if ghost’s existence is between us, they can appear both day and night. But usually, when watching TV shows about paranormal things or somebody who explains a weird success, all those phenomena happen at night.
If speaking about vampires it could have sense, because they don’t like the sun even with sunglasses. But when speaking about dark shadows, ghostly apparitions it has not sense that they only appear at night. Why do they wait to the night day to appear? Do they fear the sun light as vampires do?
Really I have not found a convincing answer surfing on the Internet. The only thing I found are silliness like: “They are tired in the morning after wandering all the night”, “you can’t see them when there is light because they are transparent.”
The only theory which comes to mi mind to explain this phenomenon is that it might be that as we are more relaxed at night and there is less noise we can be more aware about what happens around.