Set it in Tools, Options, Preferences, Calendar Options, Calendar Work
week settings.

christophercbrewster via OfficeKB.com wrote:
I know about that button. What I want to do is set "working hours only" as a
default, instead of having to set this each time I use the scheduler. I use
it frequently just to see people's schedules on a given day.

Brian Tillman wrote:

My apologies. I missed the fact that you were on the Scheduling tab of a
meeting request. As you say, on that tab, only your working hours are
shown and they're not colored any differently for Outlook 2003. I'll look
at Outlook 2007 when I get home.

I looked at Outlook 2010 and below the list of attendees on the let side of
the meeting request window is an Options button. Clicking that allowed me
to specify that Outlook should show only my working hours. I'll look at
Outlook 2007 as soon as I can.