Add a plus 1 from us as well.
We either have dashboards, with hour, 6 hours, 12 hour, 1 week etc.. or keep changing the dashboard date periods for individual widgets.
May be the period on a widget could be a "from dashboard" in addition to last value, or 6 weeks etc...
Then the you can select the period for all widgets on the dashboard using "from dashboard" to set their current value.
Leaving any widgets that are not "from dashboard" alone.
Just my 2c worth