For every news has a time when it will come out. So, the verse means, ‘do not hasten happenings, for they will come in due time, as they have their appointed times to occur.’ For example, when Allah (swt) sent down this verse:

سَيُهْزَمُ الْجَمْعُ وَيُوَلُّونَ الدُّبُرَ

((Soon) their united front will be defeated and (forced to) flee.) (Al-Qamar: 45)

Umar bin al-Khattab (may Allah be pleased with him) found it strange, as the Muslims were of those deemed weak in Mecca. But subsequently, he saw this occur before his eyes in the Battle of Badr.

Likewise, they saw the news in these following verses happening with their own eyes:

 غُلِبَتِ الرُّومُ (2) فِي أَدْنَى الْأَرْضِ وَهُم مِّن بَعْدِ غَلَبِهِمْ سَيَغْلِبُونَ

(The Romans have been defeated (2) in a nearby land. Yet following their defeat, they will triumph.) (Ar-Room: 1-2)

These examples show the meaning of: (For every happening is a finality;) So, do not hasten occurrences.