Windows Task Scheduler – Run only during window of time

Set a daily schedule starting at 5pm. In the Advanced dialog, click Repeat task, then specify Every=15 minutes, Until:Time=5am.

Edit: The above instructions are for Windows 2003 Server or XP. If Windows Server 2008 is like Windows 7, then you can do the same thing through the Triggers tab. Set a daily trigger, Start=5pm, Repeat Task Every=15 minutes, For a duration of=12 hours.
You don’t need to stick with the pre-defined times – you can type into these fields any value you wish.