I created a dashboard using Simple XML under Splunk 6. I created a search "* | stats count | addinfo | eval date=strftime(infomintime,"%B %d %Y") | fields date" and currently use a single value box. I would prefer to put that date at the top of the dashboard in the label. I need to use Simple XML so I can email the report daily to the end user.
You won't be able to change the <label></label> value that populates the form/dashboard title using Simple XML. However, you can change the value that populates the title of a panel if you convert to using a form search. Here's a working example:
Basically, I created a dropdown that replaces the time picker and allows you to choose the start date for your form. You can use the time picker and it's $earliest$ token instead but the value placed into $earliest$ will be something like -30d@d which isn't helpful as the date to be displayed in the panel title.
If you need to specify a start time different from some day at midnight, you'll just have to be sure you also modify the strptime() parameters. Also, it would be simple to add a second dropdown to specify the ending date/time. Alertantively, you could add a time picker and use the $earliest$ and $latest$ tokens created by the time picker to set bounds on the date dropdown.
But the bottom line is that you can't change the title of the form/dashboard using Simple XML.