SSIS Derived Column Conditional Time Modification
So close. It'd be

time == "24:00:00" ? "00:00:00" : time


The Ternary Operator looks like (condition) ? true : false With the notable exception of the ForEach Enumerator, nowhere else in SSIS expressions are you able to use an assignment like time = "00:00:00". It'll basically be implied by whatever column or variables it's being assigned to.

If the data type of time column is actually detected as DT_TIME the above expression is likely to break because that would be outside the allowable domain for DT_TIME values but it'd actually break/fail/error at the source component level (OLE DB/ADO NET/ODBC source)