Diane Sawyer announced this morning she would be leaving Good Morning America after this week, allowing her time to prepare for taking over ABC's flagship newscast. World News, on Dec. 21.

But the move does more than give Sawyer time to figure out how she'll make her transition smoother than the last person to take a network news anchor job, CBS rival Katie Couric. It also puts some space between her debut and current World News anchor Charles Gibson's final day on World News Dec. 18.

Such anchor transitions are always an exercise in deft maneuvering, allowing enough space between transitions so each anchor gets the full measure of press and public attention possible. Before Sawyer takes over World News, Gibson needs to get a grand finale; still left unscheduled is the ascension of her replacement on GMA, widely presumed to be This Week anchor George Stephanopoulos, who is reportedly negotiating details of the job.

It will be interesting to see how all this lines up, especially with such important transitions planned just before the holidays, when TV viewing is often disrupted.