Some words contain a madd letter before a vowelled consonant. In connected recitation, that final vowel is pronounced. At a pause, the final vowel disappears and the consonant becomes still. The resulting prolongation is called madd ‘arid li-s-sukun, because the sukun is incidental to stopping rather than original to the word.
In «الْعَالَمِينَ», the final nun is vowelled when joined to following text. If the reciter stops, nun becomes still after madd ya.
The traditional rule permits options of qasr, tawassut and tul—shorter, medium and longer measures within this specific category. Original and temporary sukun are therefore not identical. If the final vowel is pronounced in connection, the particular stop-induced cause is absent.