I am getting educated on the 10 year t-note. The electronic version (ZN). The ES mini rollover is two weeks from today (going from the March contract, to June). I was following the March contract for ZN today, and the volume was 122,000+ contracts. However the June volume was 392,000. So obviously the volume is now in June contracts. Question? When was the rollover date from the March to the June contract? Is the rollover date similar to the ES mini, meaning is it a set date following (or preceeding) some specific event or date?