If I understand your question correctly, you should be able to pick a specific time period for your time series graph by going to Add Widget on your Dashboard, then extending out "Time Range" at the very bottom, and then checking both checkboxes. Once you check the bottom checkbox "Use specific-widget time frame" this will override the user's time range in the top-right. I think it defaults to 15 mutes, so you'll want to click on the drop down that appears (where it says "last 15 minutes") and then click "Custom" > + (plus) sign, and add whatever date/time range you want. The other checkbox you checked should display the date selected in the top-right hand corner of the widget. The graph's x and y-axis' will autoscale to the time range you selected and how big you make the widget, if I recall correctly.
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