You could say something like 'from 9 hours after the restart', or 'after 9 hours from the restart', if I have understood your meaning correctly. You are correct that we don't like to repeat words, so it would be natural to avoid repeating, but it is not incorrect to use the same word twice, especially if you need to be clear about your meaning.

The first 'after' changes the meaning slightly. Without it the sentence gives a more exact time, exactly nine hours after the restart. In some contexts using the first after could suggest more than nine hours, depending on what else is said