Adjust your Work Hours in Outlook
It is possible to adjust your "work hours" in your calendar to automatically show the time you start and finish a work day. This can also affect booking a new Meeting, like teleconferencing meeting rooms, because the meeting room will be hidden as "unavailable" when trying to reserve outside of your work hours.
To change your Outlook Calendar Work Hours:
In Outlook, click on File --> Options
Select Calendar on the left menu
In the Work Time section, under Work Hours, adjust the Start Times and End Times as required. Please note that you might need to also select Sunday and Saturday as well if you need to book Meeting Rooms on the weekend.
Click OK to save the changes
Now when booking a Meeting outside of normal working hours, there should be some room availability.