There is an interesting article at the National Geographic website about the diving habits of giant squid and sperm whales. Here is a snippet of the results:
During the day the [sperm] whales and [giant] squid spent about 75 percent of their time at depths ranging from 600 to 1,300 feet (180 to 400 meters).
At night, the tagged squid spent at least half of their time above 600 feet (180 meters), most likely following small fish and other prey that migrate toward the surface at night and then return to deeper waters during the day.
Unlike the squid, however, the sperm whales only slightly altered their diving pattern at night, continuing to spend most of their time at lower depths.
Here is another interesting quote relating to the amount of squid eaten by sperm whales:
The animals have a voracious appetite for squid. Researchers estimate that more than 110 million tons (100 million metric tons) of squid - equivalent to the entire annual harvest of all the commercial fisheries on Earth - may be consumed by sperm whales every year.
Here is a link to the full article: