Most networks provide time within their programs for the program provider, either satellite or cable, to insert their own commercials. That's usually part of the compensation arrangement for carrying the network. However, the networks have to give the timings to the provider as to when to insert the commercials. That information is entered into a computer and it automatically inserts the commercials at the designated time. If for any reason the network timings are wrong, and it can be just a second or two, then the commercials will run either early or late cutting off part of the program.