So I tried this and it does not work.
(TMLMOD1 == "") ? NULL(DT_DBTIME2,7) : (DT_DBTIME2,7)(SUBSTRING(TMLMOD1,1,2) + ":" + SUBSTRING(TMLMOD1,3,2) + ":" + SUBSTRING(TMLMOD1,5,2))
I get the error below. I made sure one row had a null value in that field. Nulls on source and destination have been checked and unchecked to see if it would work, but it doesn't. as soon as I enter data in that field, it works again.
[Derived Column [2]] Error: SSIS Error Code DTS_E_INDUCEDTRANSFORMFAILUREONERROR. The "Derived Column" failed because error code 0xC0049063 occurred, and the error row disposition on "Derived Column.Outputs[Derived Column Output].Columns[TMLMOD]" specifies failure on error. An error occurred on the specified object of the specified component. There may be error messages posted before this with more information about the failure.