How does Mint define total and unique visits?
Total represents the total number of requested pages in a given timeframe. Unique represents the total number of unique visitors within a given timeframe.
The timeframes represented in the Visits pane are independent of each other. The sum of total and unique visits of the hours in a day will not necessarily equal the total and unique visits in that same day.
Why? Here’s an example:
I visit your site for the first time ever at 9am on a Monday. Both total and unique increase by one for the 9am hour and for Monday. Then say I return to your site at 11am. Both total and unique increase by one for the 11am hour but I have already visited your site today (Monday) so only the total increases by one (I can only be a unique visitor once for a given timeframe).
This logic applies to all timeframes in the Visits pane.