Is there a free graphical library that supports Gantt charts with units of hours or even minutes? I've tried a few. JFreeChart was among the most promising but scaling down seems to reduce the maximum timescale represented to just a few days.
JFreeChart should be able to go deeper that days. SimpleTimePeriod can represent time down to the millisecond. Might just need to adjust the time display of the axis from the plot.