Date masks on OUTPUT Report Page Headings can be controlled by means of a
System-Parameter, or Application-override Date masks, and an environment
variable 'APPX STD PGH MASK'.

For Example:

If I have no System or Application date mask override set, and I run an
OUTPUT with a standard page heading, I get a page heading date (for example)
of "03/25/1999 00:16 23.83"

If I had set my System or Application date mask to 

"06/05/07 - 04:03:02.01"

I get a page heading date of

"03/25/99 - 00:16 23.83"