While random() will generate a random value every frame, this variation allows you to control how often the values are generated, allowing you to effectively slow down the effect.
Code Sample
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myStart = framesToTime(0); // replace the 0 with the frame number at which you want the expression to start.
frames = 3; // the number of frames you want to hold each random value.
seed = Math.floor((time - myStart)/framesToTime(frames)); seedRandom(seed,true)
random(min, max) // specify your value range