In Outlook 2003 and earlier versions, no. In Outlook 2007 with Exchange '12', yes.

Signature
Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Is there a way to set your normal non-working hours (e.g., 5 PM to 8 AM) so
> that if somebody attempts to schedule a meeting during this time, they are
> informed that you are unavailable? The Tools->Options->Calendar Options
> window allows you to set a standard "Start time" and "End time", however,
> this only appears to change the background color for those hours on your
> calendar and is not visible to other users.