Graeme:Is this namespace always set to the date and time that the template was first saved?
For forms created from a blank data source, it will be http://schemas.microsoft.com/office/infopath/2003/myXSD/, followed by the date and time (GMT) the template was created (not saved).
Does it ever change?
No.
Can I find it from within IP or do I always need to save a form as xml in order to see it?
Right-click any node in your main data source, select Properties, and then Details.