The flag value can be retrieved as a bit value in that flags property.
Depending on which version of Outlook you're using you can get that using
PropertyAccessor (Outlook 2007) or some lower level API such as Extended
MAPI (C++ or Delphi only, no managed code), CDO 1.21 (no managed code,
possible security prompts) or a MAPI wrapper such as Redemption
(www.dimastr.com/redemption).
However that is just a flag bit that says read/unread. The time when the
item was read is not stored. It might be in the LastModificationTime
property if that was the last time the item was modified, but you have no
way to prove that.