That is true, we still have better Timestamp support for the Python (Labs) node on our agenda but did not get to add that for KNIME 4.5.2.
As for the slow data transfer with the Python Source node (non-Labs): I have tried it with KNIME versions back to 4.3 and it was also slow there, so I am curious what might have changed. Maybe the Pandas version is different? Can you tell us which Python/Pandas/NumPy versions you are using with the older KNIME installation?