Why NumberValue does not reset once it hits 0? Just goes into negatives

Like the most basic thing and i'm having a problem with it. It's just a count down thing. Two number Values and once the seconds hit 0 its supposed to go back to 60 and drop a minute. But the timer just keeps counting down into the negatives.

local min = script.Minutes
local sec = script.Seconds
local night = script.Night

while true do
    wait(1)
    sec.Value = sec.Value - 1
end

sec.Changed:connect(function()
    if sec == 0 then
        sec.Value = 60
        min.Value = min.Value - 1
    end
end)

Any help is appreciated!

Edit: Sorry I worded the title terribly. I just could not think of a way to ask this.