If you type "today" in the Finder search box, it allows you to create a search of all files that have been modified today:
and then click on Today:
And you can see, I only have 39 objects modified today:
However, if I click "Save" and save this search in my sidebar, it doesn't give me just today. Instead, it gives me all of the files on my computer, sorted chronologically. Is this a bug? Am I saving Today the wrong way? This is a useful search, but not when it provides every file.