try this ?
pvp_n_3-5,99,99,5 script Brancher 757,{
if( select( (( .Event )?"STOP":"START" ),"Cancel" ) == 1 ){
set .Event,!.Event;
mes ""+( ( .Event )?"STARTED":"STOPPED" );
}
close;
OnInit:
while( 1 ){
if( .Event && getmapusers("pvp_n_3-5") && mobcount("pvp_n_3-5","All") < 30 )
monster "pvp_n_3-5",0,0,"--ja--",-1,1; // Summon a random monster at random coordinates.
sleep 5000; // Wait 5 seconds.
}
end;
}