I am nt quite sure but i guess you can do so by using scheduled task in ms windows. You can select the file and can schedule at the time you want to run your test. If it doesn't help then post the solution if you find.
Are you working with developers? Are developers using some continuous integration system (e.g. Hudson)? If they are, you should include your test automation to be executed after each build. In that case CI system can take care of executing the tests.
At Unix-based system there is cron which can be used for timed actions if you don't have CI around but you have Linux or some other Unix-kind-of-system.
I tried using MS scheduled task to run it. I used Selenium with ruby. I scheduled at a time and It did worked :) :)
It was a graet doubt but could you tell the usage .? For what you want to run at '8 am' daily, as it would be really useful for me..
First i started selenium server by scheduled task with a batch file(I just scheduled this batch file say at 7.55 ist)
then, I started selenium client (ie., Ruby using gem install selenium-client), batch file at 7.58 ist)
then, i scheduled my testcase(test.rb) at 8.00 ist) .. Mozilla firefox opens executing the testcase. :) If you have any doubts post it or 2 my mail id firstname.lastname@example.org..