deedee: are you going to be in transit in the airport? (meaning you will leave the airplane) or you will be in the plane waiting?

If your stop/transit in Riyadh is less than 1 hr it means you will not leave the airplane then there is no need for scarf/abaaya.

So far and as to my knowledge and understanding, if you are descending in Riyadh airport you will be required to wear an abaaya but not the scarf.

On the other hand and to be absolutely assured on what to do I would suggest you to go to your airliner and ask them about the proper "dress code/etiquette" in this stop.

Regards...have a great day!!