Expertise in the Interpretation of Dreams is Bestowed by Allah on whom He wills
In the sixth verse, Allah Ta ا ala has promised some blessings for Sayyidna Yusuf (علیہ السلام) : (1) كَذَٰلِكَ يَجْتَبِيكَ رَبُّكَ (And in the like manner your Lord will choose you ...) that is, H-e will choose him for His blessings and favours, something which manifested itself when wealth, recognition and power came into his hands in the country of Egypt. (2) وَيُعَلِّمُكَ مِن تَأْوِيلِ الْأَحَادِيثِ - (and teach you the interpretation of events ...). The word: الْأَحَادِيثِ : 'al-ahadith' here means the dreams of people. It means that Allah Ta’ ala will teach him how to interpret dreams. This also tells us that interpreting dreams is a standing area of expertise which is bestowed by Allah Ta` ala on a chosen few - everyone is not fit to have it.
Ruling:
It appears in Tafsir al-Qurtubi that ` Abdullah ibn Shaddad ibn al-Had said that the interpretation of this dream of Sayyidna ~Yusuf actualized after forty years. This tells us that an instant actualization of an interpretation is not necessary either.
(3) As for the third promise: وَيُتِمُّ نِعْمَتَهُ عَلَيْكَ (and will perfect His bounty upon you), it refers to the bestowal of Nubuwwah (prophethood) upon him. And this is what has been alluded to in the later sentences: كَمَا أَتَمَّهَا عَلَىٰ أَبَوَيْكَ مِن قَبْلُ إِبْرَاهِيمَ وَإِسْحَاقَ (as He has perfected it, earlier, upon your father, Ibrahim and Ishaq). That which has been said here also indicates that the skill of interpreting dreams as given to Sayyidna Yusuf (علیہ السلام) was also taught to Sayyidna Ibrahim and Ishaq (علیہما السلام) ، peace be on them both.
At the end of the verse, it was said: إِنَّ رَبَّكَ عَلِيمٌ حَكِيمٌ (Surely, your Lord is All-Wise, All-Knowing). So He is. For Him, teaching an art to someone is not difficult, nor does He, as His wisdom would have it, teach this art to just anyone. Instead of that, He elects someone, in His wisdom, and lets him have this expertise.