If I remember correctly, the vortex sink at several hundred feet per minute and normally level off between 500 & 1000 feet below the offending aircraft. vortexs stablize around that altitude while they expand and disipate. They tend to remain about a wings span apart and all so drift with the wind. Strong winds and turbulance aloft tend to brake up the vortexs faster than if a no or light wind condition.
My personal rule is no closer than 1000 feet vertically and 5 miles in trail during cruise. Takeoff and landing minimum of 3 min. seperation and 5 to 6 miles depending on type I'm flying.