Nocturnal means mainly active at night. As for the whole cat/lizard thing I guess you could say cat-like..... but they have there own raty scheduel that they follow. Your rats will modify their scheduel so they can be up during the day with you and still keep you up at night. lol
If you want I can simplify this... just let me know.
Just remember if you get a rat you should get 2 becuase they are VERY social animals and you probably can't spend 4 hours a day with your new ratsy if you get only 1. So try and get 2 for the rats sake otherwise you will have a problem.