1. A method in a computer system for guaranteeing execution of a content image, the method comprising: under the control of an update client executing on the computer system, obtaining the content image and its associated content image policy for execution on the computer system, the content image policy specifying an approximate execution time for the content image; determining whether a service window is available for executing the content image by comparing a present time, a start time and an end time of the service window, and the approximate execution time for the content image; and upon determining that the service window is available, executing the content image on the computer system.