forward counter();

Text3D:txt;
new str[100];
new timer;
new number = 10;

txt = CreateDynamic3DTextLabel("", -1, x, y, z, 20, INVALID_PLAYER_ID, INVALID_VEHICLE_ID, 1, -1, -1, -1, 20);

public counter()
{
    if(number == 0) KillTimer(timer);
    else
    {
        format(str, sizeof(str), "%d", number);
        number--;
        UpdateDynamic3DTextLabelText(txt, -1, str);
    }
}

public OnGameModeInit()
{
    timer = SetTimer("counter", 1000, true);
}