Very funny John_2, but but your joke, as it stands, is incorrectly verschwurbelt.
In your sentence, sentence isn't in the nominative case, but rather the accusative, so verschwurbelt must also be inflected as such.
Therefore, either: ...they were just in time to hear Heidegger finish his first verschwurbelten sentence, if you're thinking of sentence as German Satz ... or alternatively: .....they were just in time to hear Heidegger finish his first verschwurbelte sentence .. if you're thinking of sentence from the point of view of its OF / Latin feminine origin...
...nur um das Verschwurbelte weiter zu verschwurbeln;-)
Thank you all for the very thorough lesson on the use of verschwurbeln/verschwurbelt !