Updated

--[[
=========CONFIGURATION=========
Add whatever maps you want below in a new column like so:
local maps={
"gm_construct",
"gm_flatgrass",
"newthing",
"anotherthing"
}
etc.  MAKE SURE IT'S BETWEEN THE BRACKETS!!!
]]
local maps={
"gm_construct", --All but last have a comma at the end
"gm_flatgrass" --Last doesn't have a comma
}
--[[
Here is the amount of time (in minutes) between each map change.
]]
local TIME_UNTIL_CHANGE=10

-----DON'T TOUCH ANYTHING UNDER HERE-----
local changetime=TIME_UNTIL_CHANGE*60
hook.Add("InitPostEntity", "startMapChange", function()
    changetime=CurTime()+changetime
    timer.Simple(TIME_UNTIL_CHANGE*60, changeMap())
end)


function changeMap()
    local map=game.GetMap()
    local ind=(table.KeyFromValue(map) or 0)+1
    if ind and maps[ind] then
        RunConsoleCommand("changelevel", maps[ind])
    else
        RunConsoleCommand("changelevel", maps[1])
    end
end

function NotifyForChange()
    local timeleft=changetime-CurTime()
    local mins=math.floor(timeleft/60)
    for f, v in pairs(player.GetAll()) do
        if mins==0 then
            mins=timeleft
            v:ChatPrint(mins.." seconds left until map change.")
        else
            v:ChatPrint(mins.." minutes left until map change.")
        end
    end
    timer.Simple(timeleft/2, NotifyForChange())
end
concommand.Add("mc_nextmap", function(ply)
    if ply:IsAdmin() then
        changeMap()
    end
end)