New setting for graphs: 1 work day = 9 h?

Hi,

in the graphs for longer periods (eg. forever) when a certain tag already has many hours, the unit of display becomes "days". It looks very much 1 day = 24 hours is used (which is correct ;-)). But I'd find it rather useful to define a "work day" time span (eg. 9 hours) that would be used here. Because being productive for 2 weeks = 10 days = 10*9 h = 90h currently displays as 90/24 = 3.75 days, which looks kinda wrong.

Thanks,
Alex!