Delayed wait time. How do I fix it?

I am trying to make a normal intermission script that will show the how long time it is left until a game round starts for example. And I have a wait time of one second. When I test the game, the wait time is not one seconds at all, it is around 3-10 seconds! Does anyone know how to fix this? Here is my code:`

for i = 15, 0, -1 do --Change '15' to your own time
    wait(1)
    t.Value = "Intermission: " .. i .. "" --Changing Text 1
    if i == 0
...