I think it's the week before Memorial Day but have not been able to confirm this.
That's probably about when. Have you tried calling the Chicago BarBri office? If they can't give you a date, it's doubtful anyone else can.
I have heard good things about MLER, but, for myself, didn't find BarBri so bad. I also did PMBR which I think was far more useful for the MBE than BarBri.