How long would such a repair take? How fast is the response time?
Response time depends on storms etc, can be months as they can't always secure the ship right away. Actual repair maybe a few days. They found the break so think they start splicing tomorrow. OTDRs help, and are surprisingly accurate.
What's surprising is how fast they can fix copper cables (terrestial). some of those have like 900 pairs in them. The newer ones are colour coded so it's not so bad, you just match up all the colours, but the older ones are not colour coded and just have paper insulation so they need to tone them all out. I'm honestly not sure how they do it as logistically it would be tricky I imagine. Two techs on a phone both toning out pairs until they find the same one I guess. The pairs may also be more or less in the same location within the cable at both ends so they must have tricks to make it go faster as they work.