Hi @tmeschke,
What you can see in in the KNIME table is just a representation/rendering of the actual date&time value. In this representation zero seconds are truncated. For further processing of that column, this does not have any impact as @mlauber71 already said. The zero seconds are still stored within the value of that cell.
If you want to have a nice representation of theses values for visualization or a report, you can convert the column back to a String using the Date&Time to String node and specify to use the “yyyy-MM-dd HH:mm:ss" format.
Let me know if you have further questions.
Cheers,
Simon