0 - 3 of 3 tags for invalid timestamp

Hi,
  I am trying to select a timestamp column in a defined format. Later on I will try and use that statement to update a timestamp column. I am using the following statement to check for the syntax but it is giving me an error of Invalid String. Please let me know what should be the correct syntax.
 

I am trying to filter transactions that are less than 5 minutes apart.  In trying to develop this filter, I keep running into error messages.  The two columns I need to find the difference for are TIME datatypes:
(SEC.CALL_START_TM-PRI.CALL_END_TM) AS TIME_DIFF

 

Goodnight

 

I have a problem doing a CAST in this query to execute, get the error invalid timestamp.
 

SELECT

(CAST( (CAST(TRIM(Stg.Fecha_Ejecucion_OOSS) AS CHAR(10)) || ' ' || CAST(TRIM(Stg.Hora_Ejecucion_OOSS) AS CHAR(8)))

AS TIMESTAMP(0))) POSTSALES_TRANSACTION_Err