Choose hour during a day in the past to plot?

I can set a date to plot with:

PlotDate=20100108;

However, regardless of what I then choose PlotBars to be, the plot region always starts on 00:00am on that day. Which parameter should I set to start the plot at a certain hour other than 00:00am in that day?

Noone knows?
This sounds like one should be able to do it though...