I want a timer to start when a TextBox has changed, but won't work. Why?

I have a TextBox and I want it to time the amount of time it takes to type in a certain piece of text, however, whenever I have used the 'Changed' function it just starts multiple timers every time the TextBox has changed. This is what I have come up with so far but can't figure out the rest. (Local script)

Code:

local timer = 0

script.Parent.enterText.Changed:Connect(function()
    while timer < 60 do
        if timer > 1 then
            print("Timer started")
            wait(1)
            timer = timer + 1
        else
            timer = timer + 1
        end
    end
end)