Vista task scheduler question

[mmoore99]

I would like to be able to use the Vista task scheduler to run a task every 15 minutes between the hours of 8:00am - 5:00pm. I have setup the task in the Task Scheduler with the following trigger:

However, with this trigger in place the task runs every 15 minutes all the time, it never stops. Am I misunderstanding the meaning of the "for duration of" setting on the trigger? If so, is there another way to accomplish the objective of only executing the tas during a specific time interval?