SQL TIMESTAMPDIFF

According the the V5R3 SQL Reference manual, this built in function should return the difference between 2 timestamps.  When I attempt to execute a statement with it, I get the error
Message ID . . . . . . :   SQL0204                                            
                                                                              
                                                                              
Message . . . . :   TIMESTAMPDIFF in *LIBL type *N not found.                 
                                                                              
Cause . . . . . :   TIMESTAMPDIFF in *LIBL type *N was not found. If this is  
  an ALTER TABLE statement and the type is *N, a constraint or partition was  
  not found. If this is not an ALTER TABLE statement and the type is *N, a    
  function, procedure, or trigger was not found.                              
    If a function was not found, TIMESTAMPDIFF is the service program that    
  contains the function.  The function will not be found unless the external  
  name and usage name do not match exactly.  Examine the job log for a message
  that gives more details on which function name is being searched for and the
  name that did not match.                                                    
 
The SQL command I am attempting to build is :
SELECT a.BBPCPK, a.BBPCPKD, a.BBASSIGN, TIMESTAMPDIFF(2,           
(DIgits(a.bbcctd) || digits(a.bbcctt)), (DIgits(b.bbcctd) ||       
digits(b.bbcctt))) diff FROM VOCTRACK a join voctrack b on         
a.bbassign= b.bbassign WHERE a.bbcctd = 20081016 and a.bbcode =    
'STR' and b.bbcode = 'END'             

The concatanation of variables for parameter 2 and 3 do result in valid timestamp values.

Was this BIF introduced later as a PTF?

The system I am using is running V5R3, but is way behind in PTF's.
I have no control over the ordering of PFT's or upgrading to a later release.

Thanks,
                            
Jeff Young
Sr. Programmer Analyst
IBM -e(logo) server Certified Systems Exper - iSeries Technical Solutions V5R2 
IBM  Certified Specialist- e(logo) server i5Series Technical Solutions Designer V5R3
IBM  Certified Specialist- e(logo)server i5Series Technical Solutions Implementer V5R3