They knew that this was going to take a while because, by the time the rescue mission began, Jumbo had drifted even further out to sea. He was much further than 10 miles out to sea by now. Since he was a living creature who needed to stay above water to breathe, they had to tow him slowly.
The rescue team knew that it would be a long process, but they had to get Jumbo to safety. The crew slowly towed Jumbo all day long. He did his best to keep his trunk out of the water from time to time to get the air that he needed.