The Time Totals section breaks down how long it takes to upgrade given the number of builders you are using. However, it is using different total times than the ones reported by the Buildings section.
For example: TH8 Builders total time is: 432d 9h 32m, at 2 Builders that would be 216d, but the Time Total section lists 224d. And at TH9 Builders Total time is 517d vs 2x405d=810d in the Time Totals section.
I'm guessing the times weren't updated for recent patches.