delay in test start although warm up time is set to zero

HI,  in my run time settings i have given my warm up time as zero hrs zero mins zero secs. and 5 iterations

after that i ran the load test and the test started immediately. but on the 2nd iteration run the test started witha delay of couple of seconds , on the third iteration a delay of 4 to 5 seconds and so on .. can someone please explain about this delay? its a bit urgent.