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Is there an expression code for random positions of repeating starting and ending fireworks effect?

I am trying to create an automated fire works show. The animation is 5 seconds flat. Is there a good random expression programming code for randomizing starting and ending positions of fire works shooting off from the bottom to the top of the screen.
I have set three key frames. And would like the trail layer to start from a random y position and shoot off into a random x & y position in 5 seconds which I will loop. Do I have to separate dimensions? And does this require a slider? Is it possible? Perhaps an if statement?
Note: I know I can do posterize time for the explosion, but the random shooting off part makes things a bit more difficult. The trail is supposed to connect to the firework position in some way.
holdTime = 5; //time to hold each position (seconds)
seed = Math.floor(time/holdTime);
seedRandom(seed,true);
random(0,1920)NULL LAYER
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temp = thisComp.layer("Null 2").effect("Slider Control")("Slider");
[value[0], temp]FireWorks Layer connected to slider