Latest news : Duda spoke to the country, but it looks like he's made a complete mess of things. He hasn't referred to the decision today, only that he took the oaths yesterday because it "reflected the will of the Sejm". Furthermore, his PhD "promotor" has spoken out against his actions, saying that it's unacceptable and that he has brought shame upon his old law department.
It looks to me like Duda is lost. He can't follow the Constitutional Tribunal's ruling without upsetting PiS and their supporters, but if he fails to follow the judgement, then he will have openly broken the Constitution - which will set him up for being humiliated in the future after he can no longer hide behind the Presidency. I bet he won't sleep very well tonight.
Trying to sum up the situation for any foreigners that might be curious about what is going on :
Today, the Constitutional Tribunal (TK) ruled that the election of three judges to the TK by the previous Sejm was lawful. They also ruled that the election of two judges was unlawful.
The TK also ruled that President Duda is obliged to take the vows of the three legally appointed judges "immediately, without delay" - which he failed to do so and still hasn't done so at the time of writing. He is obliged to follow the the rulings of the Constitutional Tribunal.
Quoting from the Polish Constitution :
The Constitutional Tribunal shall settle disputes over authority between central constitutional organs of the State.
Judgments of the Constitutional Tribunal shall be of universally binding application and shall be final.
Essentially, we have a constitutional crisis on our hands. No-one has ever defied the Constitutional Tribunal before, and the quoted articles above make it crystal clear that there's no legal possibility of doing so. If Duda doesn't receive the oath from the three legally appointed judges, then we have a very, very serious situation on our hands.
The President addressed the nation, stating clearly that he does not intend to derecognise the oath given by the three illegally appointed judges. What this means in practice is completely unclear.
Finally, December 9th - the TK will rule on whether the recent law by PiS annulling the appointments of the three now-legally appointed judges is lawful. If (as expected) - they rule that PiS only had the power to appoint 2 judges (in accordance with today's decision), it becomes an outright fight between the Constitutional Tribunal and the government. Legally, the government are wrong - but can they be forced to accept the decision of the Constitutional Tribunal?