Pearlnecklace, 4 hours? maybe at 180!! Reckon on 5 hours at a steady 140 (in Saudi) to the causeway - I did it in May. 8 hours max to Dubai - did it last November. Queues are not too bad at Qatar border and UAE border unless you get a Saudi being searched. Causeway queues are unpredictable, however Friday morning up till 11 is usually quite clear.
Also worth noting is that there are NO speed cameras between Qatar border and UAE/Bahrain borders. Sometimes Saudi speed trap under bridge at Abqaiq. Happy driving!