A summary function to be called on the process time of a specific activity, e.g. mean, median, min, max
units
The time unit in which processing time should be presented (mins, hours, days, weeks, months, quarters, semesters, years. A month is defined as 30 days. A quarter is 13 weeks. A semester is 26 weeks and a year is 365 days
color_scale
Name of color scale to be used for nodes. Defaults to Reds. See Rcolorbrewer::brewer.pal.info() for all options.