How do I randomise the math.random number each time? I get the same number each time for an object

Hello,

So I am making a game, in which when you click on the item on the floor, it will disappear between 2-4 minutes. However, when I tested this out, the item was set to invisible for lets say 132 seconds, but once it reappeared, when I pressed it again, it disappeared for 132 seconds.

The question I want to ask is if you can actually make it invisible for a different amount of time each time the item is clicked. So I don't want it to disappear for 132 seconds every time, because for the more "common" items, people can just camp them. I want it to have a random rate but I'm not sure how.

--Variable Definition
local cc = script.Parent
local candycane = game:GetService("ReplicatedStorage").candycane
local cd = cc.ClickDetector
local randomnumber = math.random(120,240)

--Main bit
cd.MouseClick:Connect(function(player)
    local bp = player.Backpack
    if not bp:FindFirstChild('candycane') then
        candycane:Clone().Parent = bp

        print(randomnumber) -- this is so I can see how long it's disappeared for. 
        wait(1)
        cc.Handle.Transparency = 1
        wait(randomnumber)
        cc.Handle.Transparency = 0
    else 
        print "already in backpack bro ,what ya doing fam, you stupid boy"
    end
end)

So what I did was i defined math.random(m,n) at the start, then referred to it after I set the handle Transparency = 0

So every time I start running the script again, the time (for example) is 165, and the item is invisible for 165 seconds (after being clicked on), then it is visible again. But when i click on it again, the time it disappears for is 165 again, which I don't want to occur. I want these items to be Legendary, so the spawn rates are random and I will add in a script which will move the object.

However this only happens for one item. So the candy cane I have in this script spawns at 182 seconds (using math.random) but when it reappears, it disappears for 182 seconds, but i want it to disappear for a different number

So can someone help me? Every time I click the item, the number from math.random i get is like (another example) 182, then I want it to generate another random number, and not use 182 again.

Thanks, Tony V