[livests]

i already try

new timer;
public CountingDown(playerid, time)
{
if(time != 0)
{
new string[5];
format(string, sizeof(string), "%d", time);
GameTextForPlayer(playerid, string, 1200, 4);
timer = SetTimerEx("CountingDown", 1000, true, "ii", playerid, time-1);
}
else
{
GameTextForPlayer(playerid, "~g~Go!", 2500, 3);
TogglePlayerControllable(playerid, 1);
SendClientMessage(playerid, -1, "Go!");
KillTimer(timer);

}
return true;
}

and
SetTimerEx("CountingDown", 1000, false, "ii", playerid, time-1);
SetTimerEx("CountingDown", false);