I exchanged comments with a user a few minutes ago regarding the reputation cap and he said he thought he was going to get the Mortarboard badge for his activities today, but he wasn't sure. I went to his profile to check, but the reputation tab only on a user profile only allows you to select a range of 2-90 days. If you try to set the range to a single day, the graph doesn't do anything - it still shows the old list of "reputation items" and it doesn't even give you an error to tell you what's wrong.
If you only want to see your reputation for the current day, you can simply set "today" as the lower bound, and some date in the future as the upper bound. If you want to check a date in the past, you're out of luck.
I think there should be an update to allow you to set a single date range like you can do on the Recent page.