The options on the top row - Today | Yesterday | The day before yesterday correctly go from 00:00 to 23:59, but the options in the bottom row : Last day | Last 7 Days | Last 30 Days | Last 90 days go from "now" back in 24 hour periods.
If I run the reports now at 12:41 local time here's what I get:
- Today - May 26, 00:00 to May 26 2010, 23:59
- Yesterday - May 25, 00:00 to May 25 2010, 23:59
- The day before yesterday - May 24, 00:00 to May 24 2010, 23:59
- Last day - May 25, 12:41 to May 26 2010, 12:41 -
- Last 7 Days - May 19, 12:41 to May 26 2010, 12:41
- Last 30 days - April 26, 12:41 to May 26 2010, 12:41
- Last 90 Days - February 25, 12:41 to May 26 2010, 12:41
The options that start with Last are going back in 24 hour periods from "now" rather than starting from the end of yesterday, and going x days back.
I would also add that a Last month would be helpful as well, using the last complete calendar month that has passed. If I ran Last month today, I would expect to see all of April.