In the current version of Splunk, this can be accomplished without having to edit any XML. Simplest steps are as follows:
In your dashboard, from the "Edit" dropdown, choose "Edit Panels".
From the "+ Add Input" dropdown, choose "Time". This adds a time picker to the dashboard.
For each panel that you want to be affected by the time picker, click the magnifying glass dropdown and choose "Edit Search String".
In the "Time Range Scope" section, choose the option that starts with "Shared Time Picker".
Click "Save" for the panel. If there are more panels to attach to the time picker then go to step 3.
Click "Done" for the dashboard.
More information at http://docs.splunk.com/Documentation/Splunk/6.2.5/Viz/FormEditor.
... View more