The study was conducted to determine the best time for harvesting the fruits of four olive cultivars in North Sinai- Egypt, to help olive farmers obtain the highest oil yield and quality under current climate fluctuations. This experiment involved fruit harvesting of four commercial olive cultivars (Picual, Manzanillo, Koroneiki, and Chemlali) on four different dates, (5th October, 19th October, 2nd November, and 16th November). The results showed that the maturity index (MI) varied between cultivars. Manzanillo fruits mature more than 15- 30 days earlier than other cultivars. Late harvesting dates recorded the highest maturity index compared to early harvesting dates. Oil concentration was cultivar-dependent but has been affected by climate change. The olive cultivars were arranged in descending order based on their oil content as follows: Chemlali, Koroneiki, Picual, and Manzanillo. The oil content also increased with increasing fruit maturity and then decreased significantly with increasing maturity index. Phenol, chlorophyll, and carotene content decreased as the ripening stage progressed, while the acidity and peroxide content increased. The most suitable harvesting dates were determined based on the maturity index, oil content, and total phenolic content. We recommended that the best time to harvest was 19th October for Manzanillo which can be two weeks early in hot seasons, in the second November for Picual, and Chamalali, and from 2 to 16 November for Koroneki.