FYI...a co-worker helped me resolve my issue. I set both $CDHDR_Last_Run_Date_Time and $Run_Date_Time to varchar(14) and in the format of 'YYYYMMDDHHMISS'.
Then here's my ABAP data flow where clause:
CDHDR.OBJECTCLAS in ('DEBI', 'KRED', 'MATERIAL')
and ((CDHDR.UDATE || CDHDR.UTIME) > $CDHDR_Last_Run_Date_Time_Char)
and ((CDHDR.UDATE || CDHDR.UTIME) <= $Run_Date_Time_Char)
Here's selected contents of the generated ABAP file (*.aba):
PARAMETER $PARAM1(14) TYPE C.
PARAMETER $PARAM2(14) TYPE C.
...
DATA ALTMP1(512) TYPE C.
DATA ALTMP2(512) TYPE C.
...
concatenate CDHDR-UDATE CDHDR-UTIME into ALTMP1.
concatenate CDHDR-UDATE CDHDR-UTIME into ALTMP2.
IF ( ( ALTMP2 <= $PARAM2 )
AND ( ALTMP1 > $PARAM1 ) ).
Since in the generated ABAP file all of the fields are varchar with concatenated date and time, I can easily pull the CDHDR deltas.
-Brad