I have artisans for the same craft, 2 are gray border one from choosing that craft and the other I don't remember. The third is a purple elite from spending a legacy credit. Their completion times are really weird.
Gray #1 has +25% speed and a task takes 8 min
Gray #2 has -25% speed and the same tasks takes 13 min 20 sec
Calculating from these the normal speed would be 10 min 40 sec
The purple elite has -75% speed and the task takes 40 min
This is not -75% (which would be 18 min 40 sec) it is -275% - yes that is two hundred and seventy five.
0