the catalytic converters in question are the 2 integrated into the exhaust manifold.
If you have an exhaust leak up top where the upper O2 (Air fuel) sensor is reading it's possible that is the cause.

failed/failing cat will read throw a code for a system below efficiency code (which is also common for a bad lower o2 sensor).

To answer your question on why it took driving around is because before a fault code is logged it goes through a few cycles to make sure the reading it was seeing wasn't an anomaly, not to mention it probably likely that you pulled the battery when doing this work? If so, that would have reset your system and it needs to go through a few driving cycles to reinitiate itself.