Krish,
I think, you can use the Customer Enhancement - CATS0006 CATS: Validate entire time sheet, to validate the user input in CAT2 transaction & populate Error messages based on your validation criteria.
FUNCTION EXIT_SAPLCATS_006.
*"----------------------------------------------------------------------
*"*"Lokale Schnittstelle:
*" IMPORTING
*" VALUE(DATEFROM) LIKE CATSFIELDS-DATEFROM
*" VALUE(DATETO) LIKE CATSFIELDS-DATETO
*" VALUE(SAP_TCATS) LIKE TCATS STRUCTURE TCATS OPTIONAL
*" TABLES
*" CHECK_TABLE STRUCTURE CATS_COMM
*" I_MESSAGES STRUCTURE CATS_MESG
*"----------------------------------------------------------------------
INCLUDE ZXCATU05.
ENDFUNCTION.
Please check & see if it works.
Thanks,
Kishor.