The nation of Prophet Younas (sws) was so close to final judgement of Allah resulting in divine punishment with which they would’ve been eradicated from the face of this earth. It is their last minute faith in the Prophet due to which they bought respite to live till a period of time the way all nations live for a certain period of time. It is an expresion of how their faith bought them this life and in it there was a warning for the Quraish i.e. they can only live now if they profess faith. All nations have a certain period of time on the face of this earth before they are either destroyed naturally or through divine punishment of a Prophet (Rasul) after itmam-e-hujjat as can be seen in Quran:
وَإِن مِّن قَرْيَةٍ إِلاَّ نَحْنُ مُهْلِكُوهَا قَبْلَ يَوْمِ الْقِيَامَةِ أَوْ مُعَذِّبُوهَا عَذَابًا شَدِيدًا كَانَ ذَلِك فِي الْكِتَابِ مَسْطُورًا (58:17)
And there is no nation which We shall not destroy or sternly punish before the Day of Judgement. That is decreed in the Book of God. (17:58)
Details can be found here:
Discussion 22313
That is why Ghamidi Sahab has translated it in the meaning of respite (مہلت) in Al-Bayan:
فَاٰمَنُوۡا فَمَتَّعۡنٰہُمۡ اِلٰی حِیۡنٍ ﴿۱۴۸﴾ؕ
پھر وہ ایمان لے آئے تو ہم نے اُن کو ایک مدت تک رہنے بسنے کی مہلت دے [91] دی۔
(Quran 37:148)
(Al-Bayan: Javed Ahmed Ghamidi)
___________________________________
[91] اِس میں قریش کے لیے تہدید ہے کہ دنیا میں رہنے بسنے کی مہلت تمھارے لیے بھی ایمان کے ساتھ مشروط ہو چکی ہے۔ لہٰذا نہیں مانو گے تو اُسی طرح زمین سے مٹا دیے جاؤ گے، جس طرح تم سے پہلے رسولوں کے مکذبین مٹا دیے گئے۔