The Lab Management extension in ALM 11.5 and beyond is the only way to set a background task through the UI to run tests without a user being logged in to the UI.
You can also use a program that interfaces to ALM through the OTA API. The program starts the test execution. You use scheduling software, like Microsoft Task Scheduler, to schedule the program to run at the desired time.
Anshoo Arora provides information on a version of that program here
http://relevantcodes.com/executing-qc-testset-via-ota-api-qcruntestset/
Or you can find a version of that program in the HP support knowledge base here