When you look at the stats for how many views you have gotten in 1 day, it is not actually how many views you have gotten since 12am. It is how many views you have had in the past 24 hours. So for example, if you look at your stats at 2pm on Monday, it is telling you how many views you have gotten since 2pm on Sunday. They fluctuate because when you check them, the 24 hour span changes and it is very common to get different amounts of page views per hour. Especially since some hours are more popular for web searching than others.
Hope that made sense and helped answer your question :)