Hello,
This is not GeniusConnect related, but Outlook related.
Whem you mark an event as "ALL DAY event", Outlook sets the end date one day later.
Example:
Some All DayEvent
Start date: 2008-dec-20 00:00:00
End date: 2008-dec-21 00:00:00
You can store the Outlook Flag "AllDayEvent" to your DB and check it in your queries to determinate the "real" Start and End.