I'm sure it's percentage with a 50% cap; before job points they lasted 3:00 for me with both pieces equipped.
I'm not exactly sure if job points are counted before the 50% or after. I'm leaning towards before - with no jig duration gear equipped, I get a duration of 2:03 with three job points, and with both pieces of gear I get 3:04 every time. Leads me to believe that it's really 3:04.5 rounded down, but someone who has more job points in that category can easily say more conclusively.