I don't think it is man hours because in the article it says
Maintainers working with field support engineers from Lockheed Martin and Pratt and Whitney set out to find a way to replace the fuel line without removing the engine.
Crew chiefs determined they could access the part through a hole just big enough to fit a hand. The location of the fuel line is nearly impossible to see. They needed to detach and set aside another component without removing it, making room even scarcer.
When the OTI was first accomplished, the fuel line swap took about 24 hours, 12 hours less than removing the entire engine and performing the maintenance on a stand. As they repeated the task on additional aircraft,
so if you only have a single hand access and that takes 24 hours, but 36 man hours works out less when you spread them across the team, then you would pull the engine as it's a quicker fix. I suppose the thing is the jumping bean version with the front lift fan etc.