You need to have "store per-minute data" enabled on "Database - Admin" tab. Otherwise only hourly data is permanently stored. When you switch to export of hourly data it should be in sync what you see in the database.
The store per-minute data is now enabled. A little rain (0.01 inches) fell yesterday around 6:58am. All 3 weather servers with the uploaded data show it. Here is a screen scrape from Wunderground:
Looking at the data in the Pro2, the rainfall appears at 6:58 and then disappears at 6:59.
Per chance, is the data only stored to the nearest 0.1 inches?
As used in a Template then it will be relative to the Resolution setting. Using a 1 minute resolution then the total is for the minute, if using say a 10 minute interval then it's for the 10 minutes. If you were using say a Month [Time Frame] and Resolution set to [Days] then that would be the total for each day.
Outside of a Template then the selectors hoursum, sumday/daysum, monthsum, yearsum, alllsum and ydaysum applied to rain0total as well as specific use of sum.. provide varying intervals directly.