they are not legally obliged to do so
It's my understanding that if they declare stan nadzwyczajny (a broader category that includes 'stan wyjątkowy') then the election has to be postponed as the constitution says:
"W czasie stanu nadzwyczajnego oraz w ciągu 90 dni po jego zakończeniu .... nie mogą być przeprowadzane ... wybory Prezydenta Rzeczypospolitej"
Of course PiS thinks of the constitution as toilet paper so it will be interesting to see if they purposefully avoid declaring a state of emergency for the sake of the elections (as happened in Iran) or try to justify not postponing the elections in clear violation of the constitution....