A date range on a dashboard can be overridden for all reports in unison by clicking on the calendar icon in the dashboard header menu shown below.

Note a view user is unable to toggle dates.

Explore users will be shown the below:

Select the desired date range, either from the list of popular options, by defining a date range or selecting a custom date range.

The new date range will be applied to all the dashboard reports temporarily. The new override date range will show in orange shown in the image below.

There are 2 ways of returning back to the default:

1) Clicking on the cross to the right of the orange date range

2) Navigate back into the date range picker and press the red 'Remove'

Note an explore user cannot make a permeant change to a date range.

For regular user and above there's an addition button to 'Save to X report(s)' shown below.

This will save over any preset date range and act as the new default date range. The 'Preview' button is the same as above and acts as a temporary update.