TOKYO — The Japanese Coast Guard said on Monday that a deadly collision between a container ship and a United States Navy destroyer had occurred nearly an hour earlier than previously believed, adding that it was investigating whether there had been a delay in reporting the crash.

The ACX Crystal, the 29,000-ton Philippine ship that collided with the destroyer Fitzgerald off Japan, reported the collision at 2:25 a.m., said Tetsuya Tanaka, a Coast Guard spokesman. Crew members said the collision, which killed seven American sailors, had just occurred, so the Coast Guard estimated that it had happened around 2:20. a.m.

But Nippon Yusen, the Japanese shipping company that chartered the ACX Crystal, determined after further investigation that the collision had actually happened around 1:30 a.m., and the Coast Guard has amended its information to reflect that, Mr. Tanaka said on Monday.

Ryota Kowata, a spokesman for Nippon Yusen, said he did not think the crew members had originally reported the collision as having happened at 2:20 a.m. “But if it was reported in that way, I now assume that was due to so much conflicting information in such a chaotic situation,” he said.