I'm not sure if you mean this, but i made a spawnprotection with a countdown timer. Here it is modified for your needs, just call the thread whenever you need it (im assuming you want the game to end when the timer expires)
Code:
spawnProtection() //called on spawn
{
self.protectiontimer = createTimer( "hudsmall", 1.0 );
self.protectiontimer setPoint( "CENTER", "BOTTOM", 0, -100);
self.protectiontimer setTimer( 600 );
self.protectiontimer.color = (0.8,0.8,0.8);
self.protectiontimer.foreground = true;
self.protectionTimerText = self createFontString( "default", 1.5);
self.protectionTimerText setParent( self.protectiontimer );
self.protectionTimerText setPoint( "BOTTOM", "TOP" );
self.protectionTimerText setText("Game ending in:");
wait 600;
self.protectionTimerText destroy();
self.protectiontimer destroy();
level thread maps\mp\gametypes\_gamelogic::forceEnd();
}