Yet the disbelievers will persist in doubt about this ˹Quran˺ until the Hour takes them by surprise, or there comes to them the punishment of the Day after which there will be no night (when every hope would turn into despair, and after which there will be no night to rest in).
Meaning:-
Persist: continue firmly, carry on, keep on, remain.
Despair: the complete loss or absence of hope.