how to make a script work for a certain time and then wait 20 sec before staring again?

so i have a script of 4 platforms that disappear every 20 seconds , how can i make them disappear only 7 times, 140 seconds of work then wait 20 seconds and after it start over the script and do it again only 7 times and so so so here is the script of the 4 platforms:

view source

wait(20) local platforms = workspace.PlatformsFolder -- all the platforms in a folder

colors = { --table of colors
	    BrickColor.new("Electric blue"), --Really red
	    BrickColor.new("Really red"), --Really blue
        BrickColor.new("Bright yellow"), --Deep orange
        BrickColor.new("Lime green") 
	    }

while true do
	    local color = colors[math.random(1,#colors)] 
	    print(color)
	    for i,v in pairs (platforms:GetChildren()) do 
		        if v:IsA("BasePart") then 
			            if v.BrickColor == color then 
				                v.CanCollide = false
				                v.Transparency = 1
				            else 
				                v.CanCollide = true
			                v.Transparency = 0
			            end
		        end
	    end
	    wait(20) --wait however long in between color changes
end

plsss helpppppp meee

Should fix your issue.

local platforms = workspace.PlatformsFolder
colors = { 
	BrickColor.new("Electric blue"), 
	BrickColor.new("Really red"),
	BrickColor.new("Bright yellow"),
	BrickColor.new("Lime green")
}
local Ticks = 0
while true do
	if Ticks == 7 then return end
	Ticks = Ticks + 1
	local color = colors[math.random(1,#colors)]
	print(color)
	for i,v in pairs (platforms:GetChildren()) do
		if v:IsA("BasePart") then
			v.BrickColor = color
			if v.BrickColor == color then
				v.CanCollide = false
				v.Transparency = 1
			else
				v.CanCollide = true
				v.Transparency = 0
			end
			wait(1)
			v.BrickColor = BrickColor.new("Institutional white")
			v.CanCollide = true
			v.Transparency = 0
		end
	end
	wait(20) --wait however long in between color changes
end
spawn(function()
	while true do
		if Ticks == 7 then
			wait(20)
			Ticks = 0
		end
	end
end)