This Thursday morning (March 7) at pit open the June contract becomes the front month traded in the pit. The June minis will become active then also.
It's always on the first Thursday after the first Friday. That is, it is always the first Thursday unless the first Thursday is the first of the month -- in that case it is the second Thursday. Aaron Schindler Schindler Trading
Actually it is always the 2nd Thursday UNLESS Friday is the first day of the month (like this month) in which case it is the first Thursday.