Timer

local args = {...}
local mins = 30
if args[1] ~= nil then mins = tonumber(args[1]) end

local mins30 = mins*60

local on = true
local signal = true

local function doSignal()
    redstone.setOutput("back", signal)
end

local width, height = term.getSize()
local function draw(per)
    local perw = math.floor((width/100)*per)
    local perc = math.ceil( ((width/100)*(per+1)) - math.floor((width/100)*per) )/100
    for x=1,width do
        local char = " "
        for y=1,height do
            if x <= perw then
                if x == perw then
                    if y <= perc then char = "%" else char = " " end
                else
                    char = "%"
                end
            end
            term.setCursorPos(x, y)
            local col = colors.lime
            if not signal then col = colors.red end
            term.setBackgroundColor(col)
            term.setTextColor(colors.white)
            term.write(char)
        end
    end
end

local t = 0
local percent = mins30/100
local timer = os.startTimer(percent)

while on do
    local event, p1 = os.pullEvent()
    if event == "key" then
        if p1 == 29 then
            on = false
        end
    elseif event == "timer" and timer == p1 then
        t = t + 1
        if t >= 100 then
            signal = (signal == false)
            t = 0
        end
        doSignal()
        draw(t)
        timer = os.startTimer(percent)
    end
end