I found this while pokeing around for more diaries info and well. The text below make complete sense if you have been watching it.*it isn't a post without a picture :3*

It appears that each diaries ability are also based on what the holder used to write about in there old diaries, example: Yuki's future diary can only tell what is happening around him,in his old diary he use to write about the things that were happening around him. If this is true, then that means Yuno wrote about Yuki every 10 minutes, the third might have wrote about his past victims, the fourth wrote about his investigations, the fifth may have wrote only 3 entries a day, the sixth could have been writing about the cults activities, the sevens most likely wrote about each other, the eighth wrote about the orphans, the ninth wrote about her actions and here plans most notable her escape, the tenth most likely wrote about his dogs, the eleventh possibly wrote about people or what business he has conducted, and the twelfth wrote about the deeds he thought were righteous.