I read it about 1995-96 - though it was a translation and the original book could have been published earlier. So, some facts I remember so far:
There were creatures able to go back in time several minutes. That was their naturally developed defense ability so they'd be able to escape predators. People domesticated them and the domestic 'version' of the creatures could shift time even more. If I'm not mistaken, they look kind of like an octopus, with tentacles. People used domesticated creatures for time travel.
The main character of the book got involved in a war, and there should be some spaceships and interplanetary flights. War went at the several time levels simultaneously, and the main character travels in time back and forth during the story.
There was a tablet with some words (maybe a task for him), and while the character travels time, letters become invisible by the end of the book.
As a result, the character understands something important about the planet, war, and human nature, but I'm not sure what exactly.