Duration percent complete is a calculation of duration completed against the total duration of all project tasks without regard to any work hour values. It is not used for health indicators (work percent complete is used for health indicators).
Duration of 10 days is 10x more than duration of 1 day, regardless of work hours, in terms of the duration percent complete measurement.
Another thing to keep in mind is that a duration total can be deceiving. Two 10 day tasks scheduled in parallel amount to a 10 day total schedule duration, but each task represents only 50% of the duration percent complete calculation. In other words, the percent complete duration is calculating the total value of the two tasks as 20 days.
In the example below, "Change Order Docs Review with Client" is twice the duration of "Inspect Materials," but only one-fifth of the total work hours. The duration complete calculation of one task versus the other is quite different from the percent complete based on work hours.
The completion of "Change Order Docs Review with Client" represents two thirds of the total duration of all tasks, or 66.67% of the duration. 10/10+5 = 66.67%
The completion from a work hours (effort) perspective is simply the hours of the completed task divided by the total hours. 10/50 = 20%.