They needed to take immediate action to flee Jerusalem when they saw that city “surrounded by encamped armies. ” That happened in the year 66 C.E.
إِنْ تَأَخَّرَتْ فَتَرَقَّبْهَا ،‏ لِأَنَّهَا تَتِمُّ إِتْمَامًا وَلَنْ تَتَأَخَّرَ » .‏