I recently send an items value to zabbix serwer by zabbix_sender with command

echo - itemname 1410090524 46.92910431713 | /usr/bin/zabbix_sender -z some.ip -p 10051 -s somehost -T -i -

it's a 21 items send sequentially every 5 minutes from 12 hosts. Every 21 item send in 5 min iteration should have the same timestamp in next iteration it should be +5min but for all 21 items should be the same, in zabbix GUI time is random shifted by +-3second for items send in the same iteration from the same host, that should not happen.