///api_version=2
(script = registerScript({
    name: "TimerHandle",
    version: "1.0",
    authors: ["You"]
})).import("Core.lib"); //just assumed your using core since you used value.createInteger, if not just put Core.lib in scripts folder

list = [ //put values in here, looks clean if multiple
    onGroundValue = value.createFloat("OnGroundTimer", 1, 1, 10) //use float instead of integer, its more percise yet lets you adjust from 1.0 to 10.0 like you did it
]

module = {
    name: "TimerHandle",
    category: "Misc",
    description: "Helps you to learn",
    tag: script.scriptVersion,
    values: list, //import list here so the module knows what to use

    //now the actual module
    onUpdate: function() {
        if (mc.thePlayer.onGround) {
            mc.timer.timerSpeed = onGroundValue.get()
        } else if (!mc.thePlayer.onGround /*you could add a check for water etc if you want to be faster there as well*/) {
            mc.timer.timerSpeed = 1;
        }
    },
    onDisable: function() {
        mc.timer.timerSpeed = 1; //If you disable the module while being onGround you may stay faster than vanilla, so reset onDisable!
    }
}

The issue with yours is probably the core module structure without importing core but from what you've posted i can't really tell.

Ah yes i figured out what your problem was:
you did

mc.timer.timerSpeed = Timer_Value

but it must be

mc.timer.timerSpeed = module.settings.Timer_Value.get()
//or if you are using core
mc.timer.timerSpeed = Timer_Value.get()

i suggest you read this and try simple stuff

module.on("packet", function(eventData) {

});

});